Physics Notes by Shaddy Hanna

7/25/2019 Physics Notes by Shaddy Hanna

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PHYSICSYear 12

SHADDY HANNA

EPPING BOYS HS


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DISCLAIMER

The following set of notes has been compiled by Shaddy Hanna in the years 2012-2013.

These notes were intentionally written out for personal use and NOT as a teaching resource. For this reason,bear in mind, that the quality of these notes were, and never have been, intended for publishing purposes.

Thus, due to the purpose of these notes, they are definitely not a full proof reference to the content covered in

the Board of Studies Higher School Certificate Syllabus for this subject, and should not be used as a point-of-

call reference. They were written as a personal reference and at times, cheat sheet, to help with personal

memory. On this note, use them at your own discretion.

Along the same notion, these were never intended to be sold. If you have been sold these set of notes, please

contact the seller and ask for a refund.

Finally, all ideas and diagrams expressed in this sheet are not my own and have been adapted from the

references listed at the end of this document. For more thorough explanations on any of the topics covered in

this document, refer to these textbooks.

A PERSONAL WORD FROM ME (:

If youre reading this, youre probably a year 12 student about to sit their HSC this year. You may skip through

all this, and that doesnt bother me, but if you havent, I hope this advice can be helpful.

The tip to succeeding in the HSC isnt a high ATAR. The reality is, that succeeding in the HSC comes down to

what you make out of this last year of high school, and every next one that follows. And that goes beyond the

ATAR you get. So what does make a successful year? Build your character. The rant will probably start about

now, just because I can since Im writing this, and youre choosing to read this, lol. By the way, please dont get

offended by my use of Bible quotes to back up what I believe. Im a proud Christian and profess that the

wisdom Ive learnt in the last few years of my life are straight from the Bible. I dont share them to arrogantly

bible-bash you. Again, remember, whether you choose to skip this or not, is up to you. So here goes:

Dontbe remembered as the kid who was competitive all year round, who screwed others to get themselves

ahead, or maybe, you didnt actively screw others but you chose not to help them. Im not trying to judge you,

believe me, Im the last person to do this. I just want to give you advice I wish more people he ard when I was

in high school. This quote from the bible well captures what I mean by the power of indifference:

So whoever knows the right thing to do and fails to do it, for him it is sin

Dontbe remembered as the kid who cared more about his ATAR then the people around them. Let me frame

it this way, if you were to die tomorrow, what would people remember you for? What legacy do you want to

leave behind? That you got a 99 ATAR? That you got a band 7 in Ext 2 Maths? Heres another quote from the

bible which has often spoken truth into me:

Do not store up for yourselves treasures on earth, where moths and vermin destroy, and where

thieves break in and steal For where your treasure is, there your heart will be also.

Dontbe remembered as the kid who never took anything serious. Theres a lot to reap from hard work which

extends beyond an ATAR. Hard work and diligence is what build character.

In Christ,

Shaddy Hanna


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TABLE OF CONTENTS

GLOSSARY OF KEY TERMS 5

PRACTICAL SKILLS 6

VALIDITY,RELIABILITY,ACCURACY 6

TYPES OF EXPERIMENTAL ERROR 6

SPACE 7

THE EARTH HAS A GRAVITATIONAL FIELD THAT EXERTS A FORCE BOTH ON IT AND AROUND IT 7

DEFINE

:W

EIGHT 7

EXPLAIN:GRAVITATIONAL POTENTIAL ENERGY IS RELATED TO WORK DONE 7

DEFINE:GRAVITATIONAL POTENTIAL ENERGY 7

PRAC:DETERMINE THE ACCELERATION DUE TO GRABITY USING PENDULUM MOTION 8

MANY FACTORS HAVE TO BE TAKEN INTO ACCOUNT TO ACHIEVE A SUCCESSFUL ROCKET LAUNCH,MAINTAIN A STABLE ORBIT AND

RETURN TO EARTH 9

DESCRIBE:THE TRAJECTORY OF AN OBJECT 9

EXPLAIN:THE CONCEPT OF ESCAPE VELOCITY 10

OUTLINE:NEWTONS CONCEPT OF ESCAPE VELOCITY 10

IDENTIFY:G FORCESFORCES ACTING ON AN ASTRONAUT DURING LAUNCH 11

DISCUSS:THE EFFECT OF THE EARTHS MOTION ON THE LAUNCH OF A ROCKET 11

ANALYSE:THE CHANGING ACCELERATION OF A ROCKET DURING LAUNCH 12ANALYSE:FORCES INVOLVED IN UNIFORM CIRCULAR MOTION 13

COMPARE:LOW EARTH AND GEO-STATIONARY ORBITS 13

ACCOUNT FOR:ORBITAL DECAY OF SATELLITES IN LOW EARTH ORBIT 13

DEFINE:ORBITAL VELOCITY USING KEPLERS LAW OF PERIODS 14

DISCUSS:ISSUES ASSOCIATED WITH SAFE RE-ENTRY INTO THE EARTHS ATMOSPHERE 14

IDENTIFY:THE OPTIMUM ANGLE FOR SAFE RE-ENTRY 15

CONTRIBUTION OF VON BRAUNTO SPACE EXPLORATION 15

THE SOLAR SYSTEM IS HELD TOGETHER BY GRAVITY 16

DESCRIBE:GRAVITATIONAL FIELDS 16

DEFINE:NEWTONS LAW OF UNIVERSAL GRAVITATION 16

IDENTIFY:THE SLING SHOT EFFECT 16

CURRENT AND EMERGING UNDERSTANDING ABOUT TIME AND SPACE HAS BEEN DEPENDENT UPON EARLIER MODELS OF THE

TRANSMISSION OF LIGHT 17

OUTLINE:FEATURES OF THE AETHER MODEL 17

DESCRIBEAND EVALUATE:THE MICHELSON-MORLEY EXPERIMENT 17

OUTLINE:THE NATURE OF INERTIAL FRAMES OF REFERENCE 18

DISCUSS:THE PRINCIPLE OF RELATIVITY 18

IDNETIFY:IF CIS CONSTANT THEN SPACE AND TIME BECOME RELATIVE 19

EXPLAIN:CONSEQUENCES OF SPECIAL RELATIVITY 20

DISCUSS:EVIDENCESUPPORTING THE THEORYOF SPECIAL RELATIVITY 22

DISCUSS:IMPLICATIONS OF SPECIAL RELATIVITY ON SPACE TRAVEL 22


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MOTORS AND GENERATORS 23

MOTORS 23

DISCUSS:THE MOTOR EFFECT 23

DEFINE:T

ORQUE 25

DESCRIBE:THE FEATURES OF A DCMOTOR 26

MAGNETIC FLUX AND EMF 27

OUTLINE:FARADAYS LAW 27

ACCOUNT FOR:LENZS LAW 28

GENERATORS 30

COMPARE:STRUCTURE AND FUNCTION OF A GENERATOR TO A MOTOR 30

DISCUSS:ENERGY LOSS IN ELECTRICITY TRANSMISSION 31

ASSESS:EFFECTS OF THE DEVELOPMENTS OF ACGENERATOR 32

ANALYSE:COMPETITION BETWEEN WESTINGHOUSE (AC)VS EDISON (DC) 33

TRANSFORMERS 34

DESCRIBE:THE PURPOSE OF TRANSFORMERS 34DISCUSS:HOW HEATING EFFECTS OF EDDY CURRENTS ARE OVERCOME 35

EXPLAIN:ROLE OF TANSFORMERS IN AUSTRALIATRANSMISSION 35

ACMOTORS 36

IDEAS TO IMPLEMENTATION 37

CATHODE RAYS LED TO THE DEVELOPMENT OF TELEVISION 37

EXPLAIN:THE APPARENT INCONSISTENT BEHAVIOUR OF CATHODE RAYSCAUSED DEBATE AS TO WHETHER THEY WERE CHARGED

PARTICLESOR EM-WAVES PRAC:DEMONSTRATING PROPERTIES OF CATHODE RAYS USING DISCHARGE TUBES 37

EXPLAIN:CATHODE RAY TUBES ALLOWED THE MANIPULATION OF A STREAM OF CHARGED PARTICLESDISCHARGE TUBES 38IDENTIFY:MOVING CHARGED PARTICLES IN A MAGNETIC FIELD EXPERIENCE A FORCE 39

IDENTIFY:CHARGED PLATES PRODUCE AN ELECTRIC FIELD 39

OUTLINE:J.JTHOMSONS EXPERIMENT -CHARGE/MASS RATIOOF AN ELECTRON 40

OUTLINE:MAIN FEATURES IN CRTOF CONVENTIONAL TVDISPLAYS &OSCILLOSCOPES 41

THE MODEL OF LIGHT,THE PHOTOELECTRIC EFFECT AND BLACK BODY RADIATION 43

OUTLINE:HERTZ EXPERIMENT 43

QUANTAM THEORY 45

SEMICONDUCTORS 48

IDENTIFY:ELECTRONS IN SOLIDS ARE SHARED BETWEEN ATOMS AND MOVE FREELY 48

DESCRIBE:DIFFERENCE BETWEEN CONDUCTORS,INSULATORS,SEMICONDUCTORS 48

IDENTIFY:ELECTRON-HOLE PAIRS 49

IDENTIFY:THE USE OF GERMANIUM IN EARLY TRANSISTORS (SEMICONDUCTORS) 49

DESCRIBE:DOPINGA SEMICONDUCTOR CAN CHANGE ITS ELECTRICAL PROPERTIES 50

IDENTIFY:DIFFERENCES BETWEEN P-TYPEAND N-TYPESEMICONDUCTORS 50

DESCRIBE:DIFFERENCES BETWEEN SOLID STATE DEVICES AND THERMIONIC DEVICES 51

DISCUSS:SHORTCOMINGS IN AVAILABLE COMMUNICATION TECHNOLOGY LED TO AN INCREASED KNOWLEDGE OF THE PROPERTIES OF

MATERIALS 53

ASSESS:THE IMPACT OF THE INVENTION OF TRANSISTORS ON SOCIETY 53

SUMMARISE:THE PHOTOELECTRIC EFFECTON SEMI-CONDUCTORSIN SOLAR CELLS 54

SUPERCONDUCTERS 55

IDENTIFY:METALS POSSESS A CRYSTAL LATTICE STRUCTURE 55DESCRIBE:THE OCCURRENCE OF SUPERCONDUCTORS 56


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ASTROPHYSICS 60

TELESCOPES 60

DISCUSS:GALILEOS USE OF THE TELESCOPE 60

DISCUSS:THE TERMS

RESOLUTION

AND

SENSITIVITY

OF TELESCOPES

60ASTROMETRY:MEASUREMENT OF CELESTIAL OBJECTS POSITION IN THE SKY 62

EXPLAIN:HOW TRIG PARALLAX CAN BE USED TO DERMINE DISTANCE TO STARS 62

DISCUSS:LIMITATIONS OF TRIG PARALLAX MEASUREMENT 63

SPECTROSCOPY 64

ACCOUNT FOR:THE PRODUCTION OF VARIOUS SPECTRA 64

DESCRIBE:THE TECHNOLOGY NEEDED TO MEASURE ASTRONOMICAL SPECTRA 65

IDENTIFY:THE GENERAL TYPE OF SPECTRA PRODUCED BY CELESTIAL OBJECTS 65

DESCRIBE:FEATURES OF STELLAR SPECTRA USED IN CLASSIFYING STARS 66

PHOTOMETRIC MEASUREMENTS 68

EXPLAIN:HOW MAGNITUDE CAN DETERMINE DISTANCE TO CELESTIAL OBJECTS 68

BINARY AND VARIABLE STARS 71DESCRIBE:BINARY STARS 71

CLASSIFY:VARIABLE STARS 72

LIFE-CYCLE OF STARS 73

OUTLINE:THE KEY STAGES IN A STARS LIFE 73

DESCRIBE:THE PROCESSES INVOLVED INSTELLAR FORMATION 73

DESCRIBE:THE TYPE OF NUCLEAR REACTIONS INVOLVED IN STARS 73

DISCUSS:THE SYNTHESIS OF ELEMENTS IN STARS BY FUSION 74


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GLOSSARY OF KEY TERMS

Account for State reasons for, report on. Give an account of: narrate a series of events or transactions

Analyse Identify components and the relationship between them; draw out and relate implications

Apply Use, utilise, employ in a particular situation

Assess Make a judgement of value, quality, outcomes, results or size

Calculate Ascertain/determine from given facts, figures or information

Clarify Make clear or plain

Classify Arrange or include in classes/categories

Compare Show how things are similar or different

Contrast Show how things are different or opposite

Define State meaning and identify essential qualities

Demonstrate Show by example

Describe Provide characteristics and features

Discuss Identify issues and provide points for and/or against

Distinguish Recognise or note/indicate as being distinct or different from; to note differences between

Evaluate Make a judgement based on criteria; determine the value of

Examine Inquire into

Explain Relate cause and effect; provide why and/or how

Extract Choose relevant and/or appropriate details

Extrapolate Infer from what is known

Identify Recognise and name

Interpret Draw meaning from

Investigate Plan, inquire into and draw conclusions about

Justify Support an argument or conclusion

Outline Sketch in general terms; indicate the main features of

Predict Suggest what may happen based on available information

ProposePut forward (for example a point of view, idea, argument, suggestion) for consideration or

action

Recall Present remembered ideas, facts or experiences

Recommend Provide reasons in favour

Recount Retell a series of events

Summarise Express, concisely, the relevant details


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PRACTICAL SKILLS

VALIDITY, RELIABILITY, ACCURACY

Definition Examples

Validity

Validity is how appropriate the

procedure and materials are to achieve

a desired experimental result.

Fairly testing the hypothesis

Keeping the variables to a

minimum

Reliability

Reliability is how repeatable the

experiment is. Do you get very similar

results every time?

Repeating several times and

taking the average value

Using computer simulation

Include a range of frequencies

Accuracy

Accuracy is how close the value

calculated from the experiment is to the

accepted true value.

TYPES OF EXPERIMENTAL ERROR

Random errorsare caused by unknown and unpredictable changesin the experiment

o Repetitioncan reduce the effects.

To help reduce random errors:

Correctly take measurements

Take multiple measurements (repetition increases reliability!) take averages

Systematic errorsare caused by errors in experimental equipment

o Limit accuracy

To help reduce systematic errors:

Instructions for the use of the instrument should be read and followed.

Corrections for instrument bias should be made (if necessary).


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SPACE

THE EARTH HAS A GRAVITATIONAL FIELD THAT EXERTS A FORCE BOTH ON IT AND

AROUND IT

DEFINE:WEIGHT

Mass: the amount of matter in a body, it is static and does not change with any force exerted on it or

from it.

Weight:the force exerted upon an object or mass due to a gravitational field. It is measured in

Newtons. = =

=6.67 10

EXPLAIN:GRAVITATIONAL POTENTIAL ENERGY IS RELATED TO WORK DONE

To change the gravitational potential energy of an object, work must be done in order for it to move.

To move the object against a gravitational field, energy is stored within the objects as a: = = =

o As object moves against the gravitational field, positive work is done is gainedo As object moves with the gravitational field, negative work is done as is lost

DEFINE: GRAVITATIONAL POTENTIAL ENERGY

Gravitational potential energy:the energy required to move an object from infinity (a very large

distance away) to any point in a field.

As objects move further away from earth, increases and thus gravity pulls the object towardsenergy, converting it back in to.

@ infinity is defined to be 0, therefore is considered to be negative

=


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IDENTIFY: REASONS FOR VARIATIONS IN THE VALUE OF G

Geographical location

o The earths crust shows variations in thickness due to factors such as tectonic plate

boundaries

o

The earth is not a perfect sphere (flattened at poles)

value of g will be greater at poles since they are closer to the centre

o As the earth rotates, the centripetal force is strongest at the equator.

o Density of the earth is not consistent due to elemental composition beneath the crust

Altitude

o As altitude increase, value of g decreases, dropping to zero when = 0PREDICT: TH E VALUE OF ACCELERATION DUE TO GRAVITY ON OTHER PLANETS

=

PRAC:DETERMINE THE ACCELERATION DUE TO GRABITY USING PENDULUM MOTION

Acceleration due to gravity can be determined by use of a pendulum.

= 2

Therefore,

= 4 METHOD

Measure the length string holding the mass

Make sure the swing has a max of a 30variation from the vertical Use a stopwatch to complete 10 full swings

o Divide this value by 10, to find T

Repeat the experiment with various values of Graph the results

o (should be a straight line)o Gradient = g

RESULTS

A value of 9.5 ms-1was calculated


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MANY FACTORS HAVE TO BE TAKEN INTO ACCOUNT TO ACHIE VE A SUCCESSFUL

ROCKET LAUNCH, MAINTAIN A STABLE ORBIT AND RETURN TO EARTH

DESCRIBE: THE TRAJECTORY OF AN OBJECT

Projectile:any object launched into the air

o Assumes no air resistance

o Assumes no curvature of the earth

o At max height, vertical velocity = 0

o Negative sign indicates direction

o Horizontal velocity and vertical velocity are

independent of each

Trajectory:the path a projectile follows during its flight

in the shape of a parabola

o Horizontal motion:constant velocity motion:

= c o s

= = =

o Vertical motion:accelerating motion: = s i n = = 2 =

DETERMINING MAXIMUM HEIGHT

1.

Resolve initial velocity, u, into component uy

2. Consider the vertical motion up to the peak.

3. Note that vy= 0 in this case.

4. Select an acceleration equation to suit the available data.

5. Calculate y, which will be maximum height.

DETERMINING TRIP TIME

1. Resolve initial velocity, u, into component uy.

2. Consider the vertical motion up to the peak.

3.

Note that vy= 0 in this case.4. Select an acceleration equation to suit the available data.

5. Calculate ty, time to rise to the peak.

6. Double this time to find the trip time, since it takes just as long to fall as to rise.

DETERMINING THE RANGE

1. Resolve initial velocity, u, into components uyand ux.

2. Analyse the vertical motion to find the trip time as shown above.

3. Now consider the horizontal motion and calculate the range using x = u xt.


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DESCRIBE: GALILEOS ANALYSIS OF PROJECTILE MOTION

All projectiles move in a parabolic shape

All projectiles fall at the same rate, regardless of weight

Horizontal and vertical motion are separate

EXPLAIN: THE CONCEPT OF ESCAPE VELOCITY

The initial velocity required by a projectile to rise vertically and just escape the gravitational field of a

planet.

o For an object to escape a field its kinetic energy must be greater than the potential energy.

= 2

GRAVITATIONAL CONSTANT

We can see that MASS AND RADIUS OF THE PLANET

We can see that and o As mass increases, velocity increases

o As the radius increases, velocity decreases

OUTLINE: NEWTONS CONCEPT OF ESCAPE VELOCITY

An object could be put into orbit, if it was

launched horizontally from a tall mountain.

Given enough speed, the curvature of the earth

would match the curvature of the projectiles

trajectory and thus go into orbit.

Type of orbit Velocity

Partial Elliptical < 8 Circular = 8 Elliptic 8 < < 11.2

Parabola

= 11.2

Hyperbola > 11.2


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IDENTIFY: G FORCES FORCES ACTING ON AN ASTRONAUT DURING LAUNCH

The term g force is used to express a persons apparent weight as a multiple of their normal weight.

= = o During launch:the apparent weight felt is = [gravity] [thrust]o When on earth:you are only feeling apparent weight, which=true weight, 1g.

o When in free-fall (orbit):you experience 0g since you have no apparent weight due to no

reaction force from the ground

G forces can cause:

o

A black outwhere blood rushes to their feet if accelerate on is in the direction of persons

head

o A red outwhere blood rushes to their head and retina

Humans can withstand up to 4g, yet up to 20g are tolerable for short times when:

o They were lying down (stops blood draining from head or opposite)

o Face is upwards (prevents eyes from popping out)

o They recline in specially moulded seats (maximum body support)

DISCUSS:THE EFFECT OF THE EARTHS MOTION ON THE LAUNCH OF A ROCKET

Launch Windows:A specific period of time during which a spacecraft or projectile must be launched

If a rocket is launched it will gain a boost of velocity from such factors.

o From the equator

o Towards the east (in the same direction) from Earths rotational velocity

o Favourable time of the year when orbit of earth corresponds to desired direction

This results in less fuel needing to be used


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ANALYSE:THE CHANGING ACCELERATION OF A ROCKET DURING LAUNCH

LAW OF CONSERVATION OF MOMENTUM

In any closed system, the total momentum of the system must remain unchanged. Therefore, during horizontal flight, the change in momentum of the ignited gases backward must

equal the change in forward moment of the rocket itself.

=0 = = 0 = 0 = =

= Therefore, since the mass of the rocket will decrease as fuel is burnt, velocity will increase due to the

equation.

FORCES EXPERIENCED BY ASTRONAUTS

Before take-off, the rocket is at rest and the net force = 0

o Therefore thrust must exceed the weight of the rocket body to lift=off

Acceleration > 0

g Force > 1g =

= =

= =

Since mass decreases as fuel is burn, but thrust is constant, a non-uniform acceleration is produced

= 1 Therefore since g is constant, as acceleration increases, the g-force felt also increases.


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ANALYSE: FORCES INVOLVED IN UNIFORM CIRCULAR MOTION

Centripetal force:the force that maintains circular motion, directed towards the centre of the circle.

o Uniform circular motion: uniform orbital speed which acts as a result of centripetal force

= Motion Source of Force

Spinning a ball on a string The tension in the string

Electron orbiting atomic Nucleus Electron-nucleus electrical attraction

Car cornering Fiction between tyres and road

Moon revolving around Earth Moon-Earth gravitational attraction

Satellite orbiting around Earth Satellite-Earth gravitational attraction

COMPARE:LOW EARTH AND GEO-STATIONARY ORBITS

Low Earth Orbits Geostationary Orbits

Altitude

250 < Altitude < 1000km

(just above 1000km is the Van Allen

radiation belts, avoiding intense levels of

radiation)

36000km

Velocity 27900 kmh-1 10600 kmh-1

Orbital Period 90 min 24 hrs

Orbit Surveys the entire globe Orbits fixed point

Use Weather and imaging satellitesCommunication satellites(AUSTAR

etc)

ACCOUNT FOR:ORBITAL DECAY OF SATELLITES IN LOW EARTH ORBIT

Orbital decay:the process which occurs when LEOs are affected by the upper atmosphere causing

atmospheric drag.

o Since LEOs are still in the Earths atmosphere, they collide into particles over time, causing

them to loose kinetic energy and form a more elliptical orbit over time

o Eventually, the satellite is unable to sustain the required velocity, and it spirals down to earth

at such a high speed that friction forces on the satellite burn it up.


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DEFINE:ORBITAL VELOCITY USING KEPLERS LAW OF PERIODS

Orbital velocity:the velocity of an object, as it moves in circular motion, needed to maintain a

particular orbit about a central body.

= 2 = 2 KeplersLaw of Periods:

= 4

2 =4

=

This shows that the orbital velocity of a satellite depends on the radius of the orbit and the mass of

the central planet, independent of the mass of the satellite.

DISCUSS: ISSUES ASSOCIATED WITH SAFE RE-ENTRY INTO THE EARTH S ATMOSPHERE

HEAT

The earths atmosphere provides aerodynamic drag on the spacecraft and high temperatures are thus

generated by friction with air molecules Such high temperatures can cause the shuttle to burn up and endanger astronauts

SHAPE OF ROCKET

Shape must be curve and blunt

o Creates a shockwave in front of the spacecraft

which further absorbs heat generated

o This is succeeded by entering the earth with the

nose (opposite to the blunt bottom end) facing

upwards)

LAYER PROTECTION

Heat insulators are used:

o Ablation (ablative layers)

A skin made up of fiberglass or ceramic tiles

Absorbs heat and is made to be destroyed

Createsfireball effect

o Layer of porous silica tiles that consist of 90% air spaces

Air is a good insulator

Prevents tiles from absorbing moisture from the atmosphere


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G FORCES

Extending the re-entry and slowing the rate of descent

o Control re-entry angle to avoid high g forces

Astronauts recline in contoured couches, face the direction of acceleration (upwards)

DE-ORBITING

1. Thrust against the direction of the orbital motion (decrease velocity/set out of orbit)

2.

Thrust to point the nose upwards

3.

S-turn manoeuvres to slow shuttle down (20 min before landing = high heat)

4.

Begin using wings to control lift (like airplanes)

5.

Slowed with small parachute

RADIO BLACKOUT

Heat build-up around shuttle ionizes atoms around it

o Forms a layer which radio signals cannot penetrate

o Prevents communication

o Suffers 16 minute blackout of no communication

IDENTIFY: THE OPTIMUM ANGLE FOR SAFE RE-ENTRY

Optimum angle for safe re-entry is: 5 . 2 < < 7 . 2 If angle is too shallow(a < 5)

o

Shuttle will bounce off the atmosphere (not able to penetrate atmosphere)

o Head back off into space (no fuel or direction)

If angle is too deep(a > 7)

o Shuttle will burn up in the atmosphere due to greater collisions with particles as the surface

area is more prone to particles.

o Further, this may pose greater threat to astronauts on board due to greater g-force

experienced

CONTRIBUTION OF VON BRAUN TO SPACE EXPLORATION

Von Braun was a German rocket scientist father of modern rocket science

Developed the V2 rocketin Germany for the Nazis to bomb London in WWII

o After the war, Von Braun was captured and developed for NASAUSA

Developed US first ballistic missilecalled the Redstone Rocket

o First missile to carry a nuclear warhead

Assisted the launch of the Explorer 1 satellite

o First spacecraft to detect the Van Allen radiation belt

Developed the Saturn V Seriesrockets

o Heaviest rockets launched

o Rocket was used in Apollo and the Skylab 1 mission


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THE SOLAR SYSTEM IS HELD TOGETHER BY GRAVITY

DESCRIBE: GRAVITATIONAL FIELDS

Field:a region in which something experiences a force without no necessary direct contacto e.g. Magnetic fields

Gravitational field:any point in space where a gravitational force is felt

o An attractive force

o The bigger the mass=the stronger the field

o The further away two objects are separated, the less force they exerted on each other

DEFINE: NEWTONS LAW OF UNIVERSAL GRAVITATION

Every mass in the universe is attracted to every other mass in the universe by a force of gravitation

= Satellites must have a certain velocity in order to stay in orbit

o This velocity depends on the force of gravity acting on the satellite

= IDENTIFY: THE SLING SHOT EFFECT

When a satellite travels behind another planet, it can gain a boost in speed by the slingshot effect

This is an elastic collision between the craft and the planet (where momentum/ are conserved)o The planet transfers its momentum and to the satellite Due to the large size of the planet, this change in velocity is very insignificant

o The satellite gains velocity relative to the sun

o The satellite gains a change in direction due to the gravitational field of the planet

The final effect is a substantial gain in velocity without the consumption of fuel cost-efficient


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CURRENT AND EMERGING UNDERSTANDING ABOUT TIME AND SPACE HAS BEEN

DEPENDENT UPON EARLIER MODELS OF THE TRANSMISSION OF LIGHT

OUTLINE:FEATURES OF THE AETHER MODEL

The luminiferous Aetherwas the proposed medium for light and other EM waves to travel through

before it was found that these waveforms do not need a medium in order to travel

o During the 19thcentury, Frenchman Descartes, and other scientists, believed that motion

could only be carried from one piece of matter to another through bodily contact

o Light was considered to be a compression wave

Proposed properties of The Aether should:

o Fill all of space and have a low density

o Be transparent and stationary in space

o Permeate all matter, yet be completely permeable to material objects

o Have great elasticity to support and propagate the light waves

o

Have the consistency of wax; with both solid and liquid properties

DESCRIBE AND EVALUATE: THE MICHELSON-MORLEY EXPERIMENT

AIM

To measure the velocity of the earth relative to the Aether.

METHOD

PREVIOUS METHODS

Since the Aether was known to be stationary, scientists believed an Aether wind must therefore

exit. However, due to the Aether low density, it was too hard to detect.

Many experiments designed to test the Aether wind were disregarded along the assumption that

the equipment was not sensitive enough.

MM METHOD

The experiment was set on a bed of

mercury to allow for easy rotation since

the direction of the Aether was unknown.

Light from a monochromatic coherent

light source was shot to a half-silvered

mirror, which would split the ray into two

parts, travelling perpendicular to each

other.

Half of the light would travel to mirror B,

and the other half to mirror A

Here, one of the light rays would be

slowed by the Aether wind and thus meetat the interferometer out-of-phase to reflect an interference pattern, implying the speed of the

Earth, relative to the Aether wind.

Coherent

Interferometer


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INTERPRET: RESULTS

EXPECTED RESULTS

Due to the extra distance the beam of light travelling towards A would need to travel, the waves wereexpected to be out-of-phase and thus reveal an interference patter at the interferometer.

EVALUATED RESULTS

The experiment received a null resultdespite being extremely accurate and sensitive

o It was repeated many times during the year at different locations on the earth

o Nevertheless, no interference patter was ever detected.

However, the null result did not necessarily disprove the existence of the Aether.

DESCRIBE: COMPETING THEORIES

Due to the null result, scientists further tried to modify the Aether model rather than abandon it:

o a large object such as a planet could drag the Aether along with it

o objects contract in the direction of the Aether wind

Finally, scientists eventually abandoned the theory and as Einstein proposed his theory of special

relativity, the Aether model was made unnecessary to explain the properties of light

OUTLINE:THE NATURE OF INERTIAL FRAMES OF REFERENCE

An inertial frame of reference is one that is not accelerating.

o

Therefore, it is either undergoing a constant velocity or is stationary. All lays of physics hold true

PRAC:DISTINGUISHING BETWEEN FRAMES OF REFERENCE

A simple test is to hang a mass from a piece of string and hold into it.

o In an IF of R, the mass will appear to remain stationary relative to you

o In an N-IF of R, the mass will experience force acting upon it, therefore the mass will deviate

in an angle.

An accelerometer can also be used to measure the force acting upon an object; however the force

responsible may be a result of gravity.

DISCUSS: THE PRINCIPLE OF RELATIVITY

All steady motion is relative except the speed of light cwhich is constant in all reference frames

It is impossible to detect the motion of an IF of R without referring to a point outside that frame.

o No experiment can distinguish whether an object is moving or not without such reference

EINSTEINS POSTULATES

1. The laws of physics are the same in all inertial reference frames

2.

Speed of light c is constant in all inertial reference frames Thus, space and time must become relative concepts


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Physics

Shaddy Hanna

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ANALYSE:EINSTEINS THOUGHT EXPERIMENTS

Einstein needed to use thought experiments to prove many of his theories

o Benefit:Due to the technical limitations, cost and conditions reality offers

o Limit:The expectations of the experiment are drawn from our past understanding

Imagine that you are sitting in a train facing forwards. The train is moving at the speed of light. You

hold up a mirror in front of you, at arms length. Will you be able to see your reflection in the mirror?

o Outcome 1NO

The reflection will not appear because the train is travelling at the same speed as

the light, therefore the light would not catch the mirror

This violates the principle of relativity

o Outcome 2YES

The reflection will be seen

As a result, an observer outside the train will see light travel at speed 2c

This is the result predicted by the Aether model

o

Einsteins final outcome: The reflection will be seen, because he believed the principle of relativity.

The observer on the embankment would observe light travelling as c, yet to hold

such statements time and length are dilated.

IDNETIFY: IF C IS CONSTANT THEN SPACE AND TIME BECOME RELATIVE

If the speed of light is seen to be constant, in any optical experiment the distance and time witnessed

by observers of different IF of R must be different:

=

The final conclusions were that the speed of light had to be constant, and thus space and time

became relative measurements.

DESCRIBE: THE SIGNIFICANCE OF EINSTEIN S CONSTANT SPEED OFLIGHT

His special theory of relativity than stated two postulates:

o The laws of physics are the same for all IF of R

o The speed of light is constant for all IF of R

Thus Einstein proposed the space-time continuum where any event has four dimensions (three space

coordinates [x, y and z] and a coordinate of time) which fully define their position within its frame ofreference.

o Distance and time are relative terms

o Velocity (speed of light, c) is an absolute and fundamental quality

DISCUSS:THE CONCEPT OF LENGTH STANDARDS

The metre as a unit of length was defined in

o 1875:The distance between two lines scribed on a single bar of platinum-iridium alloy kept

in a French museum with copies sent out across the world

o Current:Incorporates the speed of light as a constant where the 1 metre = the distance

speed of light covers in one second ( )


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Physics

Shaddy Hanna

20 of 77

EXPLAIN: CONSEQUENCES OF SPECIAL RELATIVITY

THE RELATIVITY OF SIMULTANEITY

Two events that appear simultaneous in one IF of R, are not necessarily simultaneous in all IF of R

THE EQUIVALENCE BETWEEN MASS AND ENERGY

As an object speeds up, it becomes heaver (seen in mass dilation)

o This is because to accelerate an object, work is done.

o

Therefore, as work is done, is increased. As the object approaches c, due to = that energy is changed into mass as an object is sped up, the energy used to accelerate becomes mass

as on object slows down, the mass is converted back into energy

Due to Einsteins = , since is such a large number, a lot of energy is needed in order toproduce only a small yield of mass and vice versa = =


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Physics

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LENGTH CONTRACTION

A direct consequence of time dilation.

The shortening of an object in the direction of its

motion, as it approaches the speed of light

o : The length of an object within its IFof R is called its real length

o : The length of an object forobservers in different IF of R is called its

relativistic length

As , 0(in the direction of motion) = 1

TIME DILATION

The slowing down of time it takes for an event

to occur, as it approaches the speed of light

o :The time taken for an event to occurwithin its IF of R is called its real time

o :The time taken for an event to occurin view of observers in a different IF of

R is called its relativistic time

As , = 1

MASS DILATION

As an object reaches a velocity of c, the mass

increases infinitely due to the Einsteins = .o :The mass recorded within its IF of

R, called its real masso :The mass recorded to an observer

outside the IF of R, called its relativistic

mass

As , = 1


23/78

Physics

Shaddy Hanna

22 of 77

DISCUSS:EVIDENCE SUPPORTING THE THEORYOF SPECIAL RELATIVITY

When Einstein released his special theory of relativity in 1905 and general theory of relativity in 1915,

the technological capability to verify such predictions had not yet existed.

Thus, as technology developed, scientists were able to prove such theories through:

o The use of very accurate atomic clocks

one clock would stay on the ground whilst the other would be flown into space over

a long distance

when compared, the clock that was flown around did slow down

o the analysis of muons

muons are particles create in the upper atmosphere by incoming cosmic rays

their life span is so short they should not live long enough to reach the earths

surface, yet they do

this is because they travel at 0.996c and due to time dilation they have a dilated

lifetime allowing them to reach the earth, and in their view the earths atmosphere

has contracted, allowing them to reach in time tooo = can be seen in nuclear reactors and atomic weapons

DISCUSS:IMPLICATIONS OF SPECIAL RELATIVITY ON SPACE TRAVEL

Mass increase

o As a mass reaches a velocity of the speed of light, the mass increases indefinitely, thus

requiring an infinite amount of force to accelerate the space craft further

o This can also pose problems on the mass of the human occupants themselves being a hazard

Time dilation

o As the spacecraft reaches a velocity of c, time appears to slow down and

o

This increases the practicality of long space journeys, making them possible for humans to

reach in a lifetime.

Length contraction

o As the spacecraft reaches a velocity of c, length contracts and thus the trip appears to

shorten.

o This making trips to distant planets more practical and possible tor each in human lifetimes

However, these are all impractical since the energy required to reach such speeds for time dilation or

length contraction to be noticeable is exceedingly high. =


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Physics

Shaddy Hanna

23 of 77

MOTORS AND GENERATORS

MOTORS

DISCUSS: THE MOTOR EFFECT

A current-carrying conductor in an external magnetic field will experience a force

Size of force on an electric charge moving through a magnetic field:

o = o = o =

=

Magnitude of force on current carrying conductor is dependent on:

o Magnetic field strength:Force on charged particle in magnetic field is proportional to

strength o Magnitude of current:Greater current means more electrons in motion, hence greater total o Conductor Length: Greater length means more electrons available to feel a force, thus

greater o Angle between magnetic field and conductor: Force is maximum at right angles to field, as ,

=

A current carrying conductor produces a magnetic field

o As a result, as it passes through an external magnetic field

both fields interact, and the conductor experiences a force

Can be determined using Right Hand Slap Rule

DESCRIBE: THE FORCE BETWEEN PARALLEL CONDUCTORS

Amperes Law: Two parallel current-carrying conductors will exert a force on each other due to the

magnetic field they product.

o Current flowing in the same directionforce will be attractive

o Current flowing in oppositedirectionforce will be repulsive

= Where

= =

= 2 1 0

= 1 = 2


25/78

Physics

Shaddy Hanna

24 of 77

DESCRIBE: FORCES ON A COIL

Forces action on the sides of the coil can be calculated by the right-hand palm rule and=o When the plane of the coil is parallel to the external magnetic field, the forces are in

opposite direction and thus will providing a turning moment

Maximum torque at this point

o When the plane of the coil is perpendicular to the external magnetic field, the forces are in

opposite direction in the same line of action and thus cancel out.

Momentum pushes the coil a little further, and the commutator changes current

direction, and thus force direction leading in a continuous spin

Zero torque at this point


26/78

Physics

Shaddy Hanna

25 of 77

DESCRIBE: APPLICATIONS OF THE MOTOR EFFECT

GALVANOMETER

Device used to measure magnitude/direction of small DC currents

o When a current is applied to the pointer, the coil turns

Spring calibrated to provide a counter-balance force

and return the needle back to the starting point

o Soft iron core to amplify force felt

o Deflects either way depending on direction of current

o Radial magnets used to provide constant torque = uniform scale

=Thus since n,B,L, , LOUDSPEAKER

Device used to produce/amplify sound

o Circular magnet with opposite poles on outside/inside

o Voice coil sits between these poles

Connected to AC current

As current direction changes, force on coil

(cone) reverses

IDENTIFY:TYPES OF MAGNETS USED IN MOTORS

Permanent ferro-magnets

o Normal Iron magnets

o Fixed to the body of the motor

Electromagnets (solenoids)

o Created by using a soft iron shape with coils of wire around it

o May access current from armature coil

DEFINE:TORQUE

The turning momentumof an object when force acts upon it

o It increases proportionally with the distance from the pivot, thus

= = = = Radial Magnetic Fields

o As 0 , 1and as 9 0 , 0 Thus, torque is maximum when the coil is

parallel to the field

o Thus, the coil will always lie parallel to the field,

providing a constant maximum torque


27/78

Physics

Shaddy Hanna

26 of 77

DESCRIBE:THE FEATURES OF A DC MOTOR

Feature Role

Axle Cylindrical bar of hardened steel providing centre of rotation for rotor.

Magnets

(stator)

Provide the external magnetic field which interacts with the internal magnetic fields

formed by the current to produce a form in the coiled wire

Can be provided by permanent ferro-magnets or electromagnets

Armature

(rotor)

Iron cylinder mounted on the axle to allow rotation motion of the motor

Carries the rotor coils.

Iron core concentrates external magnetic field.

Coil(rotor)

The insulated wire wound around the armature.

Provides medium for the current to flow

Coils provide a force/torque for the motor (rotor) to rotate (motor effect)

Split-Ring

Commutator

Consists of a broad ring of metal mounted on the axle at one end of the armature.

Metal sheets are separated and attached to each side of the armature.

Changes the direction of the current from DC supply every half-turn

Change in current direction = change in force direction (motor effect)

Brushes

Used to maintain electrical conductivity between the external circuit and the coil

via the split ring commutator

Brushes made of Carbon (good lubricant = durable = less friction)


28/78

Physics

Shaddy Hanna

27 of 77

MAGNETIC FLUX AND EMF

OUTLINE: FARADAYS LAW

Electromagnetic Induction(opposite of motor effect):the induction of an EMF required:o An external magnetic field

o A current-carrying conductor (closed circuit to conduct current)

o Relative motion (Change in rate of flux)

Cause of the induced EMF and current

o As conductor moves relative to magnetic field, the direction of force on electrons within the

conductor can be found using right-hand palm rule

Movement of electrons leaves a deficiency of electrons (a positive charge) at one

end of the conductor, i.e. there is an emf between the ends of the conductor

If this conductor is part of an external circuit, a current will flow through the circuit

DESCRIBE: MAGNETIC FLUX

Magnetic flux density, also known as Magnetic field strength, B, is the amount of magnetic flux

passing through per unit area

o Deals with the strength of the overall field

= = Magnetic fluxis the amount of magnetic field passing through a given area

= =

DESCRIBE: EMF

The generated potential difference (or voltage/EMF) is equal to the rate of change of magnetic flux.

= =

This can be interpreted graphically as the derivative of Magnetic Flux:

= []=

[]

=[sin]=sin


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Physics

Shaddy Hanna

28 of 77

ACCOUNT FOR: LENZS LAW

An induced EMF (and current) is always in a direction such that its magnetic field opposes the

change in flux that created it.

A result of conservation of energy:

o If the current induced aided the motion the conductor would thus accelerate infinitely

o Results in creation of kinetic energy which cannot happen

Thus the negative sign in the EMF equation is to note the opposite direction

EXPLAIN: BACK EMF IN MOTORS

Lenzs Law in Motors:

o Electric motors use an input voltage (supply EMF) to produce the current in the coil

o Due to a change in flux/relative motion between the coil & magnetic field an EMF is induced

o

Thus if EMF was to occur in the direction of the motor, the speed will increase infinitely Opposing the principle of conservation of energy

o Therefore, back EMF induced must oppose the direction of the supply EMF

In a motor, supply EMF is constant, back EMF increases proportionally to the speed of the motor

o In an ideal motor (no friction) the coil will accelerate until Back EMF = Supply EMFo Net EMF = 0, Law of Inertia will allow the coil to continue rotating at constant speed

=

When back EMF is low (due to slow speed/change in flux), net EMF is high.

o At start-up, the motor rotates to slowly due to inertia of the coil to spin

o When a heavy load is on the motor it rotates to slowly

o This results in the motor drawing a higher current, which can burn out the motor:

Starter Motor:smaller motor which draws less current is used to turn the larger

motor

This provides some back EMF for the larger motor when it starts up

Thus drawing less current

Load Resistorsat start-up high resistors are placed in circuit

Thus draws up current

As coil speeds up, back EMF increases, resistor is removed


30/78

Physics

Shaddy Hanna

29 of 77

EXPLAIN:THE PRODUCTION OF EDDY CURRENTS

Produced between the relative motions of a conductor

(sheet of metal) and a magnetic field

o Small circular paths of current

Direction is due to Lenzs law

o Due to resistance, the produce heat

Right hand palm rule

o Force on positive charges is to the right

Thus left (due to Lenzs Law)

Right hand grip rule

o Relative motion is moving from magnetic field

Thus induce current will oppose this

Thus will form North pole behind metal

Thus current is clockwise

EXPLAIN: HOW INDUCTION IS USED IN COOKTOPS

Formation of eddy currents:

o A coil connected to an AC supply exists below the cooktop.

o This provides a changing magnetic field (constant change in flux)

o Thus inducing an EMF (producing an eddy current) on the metal base of the pan

o Due to resistance (property of eddy currents) the pan heats up, cooking the food

Advantages:

o Cooktop does not get hotless danger of burns

o No naked flamesless danger of burns

o

Heat is produced in the panNo loss of heat

Disadvantages:

o Cookware must be made of ferrousmaterial

o Requires flat-bottomed pans

IDENTIFY: EDDY CURRENTS INELECTROMAGNETIC BRAKING

Formation of eddy currents

o Electromagnets are positioned either side of the rotating disc

o Thus there is relative motion between the conductor and the

o

electromagnetso Thus eddy currents are induced on the spinning disc

The eddy currents produce their own magnetic field

to oppose the electromagnets

Electromagnets are used since they can be strengthened, weakened and/or turned off

o The magnets induce a smaller eddy current as the speed of the disc slows

o Thus resulting in a very smooth breaking


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Physics

Shaddy Hanna

30 of 77

GENERATORS

COMPARE: STRUCTURE AND FUNCTION OF A GENERATOR TO A MOTOR

A generator is simply the reverse of a motoro Generators harness kinetic energy to produce electrical energy (by Faradays law)

Has load and external torque

o Motors use electrical energy to produce kinetic/mechanical energy

Power supply provides torque

As a coil rotates through the magnetic field, there is a change in flux and thus an EMF is induced

(Faradays Law). Due to Lenzs law the EMF is induced in order to oppose the change in flux.

o Magnetic Field is used to induce a current

Usually the rotor

o Coils are stationary situated around the magnet e.g. 3-phases generator

DESCRIBE: DIFFERENCES BETWEEN GENERATORS

DISCUSS: ADVANTAGES AND DISADVANTAGES OF EACH

Function

AC DC

Connected to circuit by slip ringsConnected to circuit by split-ring

commutator

EMF produced periodically alternates

direction (AC current) since each

terminal is connected to the same side

of coil

Current always flows in one direction

(DC current) since commutator reverses

link between terminals every half-turn

Advantages

Slip rings have a smooth surface, dontwear out fast

Many appliances use DC

No possibility of short circuits Magnetic field is stable (no back EMF)

Voltage can be stepped up/down

-use of transformers in transmissionNo shielding needed from EMR

Disadvantages

Back EMF opposes supplied EMF Commutator brushes wear easily

Emits EMR so wires need shielding Require high maintenance

AC current travels at edge of conductors

(slightly inefficient)Cannot be transmitted


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Physics

Shaddy Hanna

31 of 77

DISCUSS: ENERGY LOSS IN ELECTRICITY TRANSMISSION

As electricity is transmitted through wires, Ohmic heatingoccurs

o Energy is lost in the form of heating

= = = = =

Minimizingenergy loss:

o Low resistance conductors

o Step up transformers

o Thick conductors (=less resistance)

IDENTIFY:PROTECTION OF TRANSMISSION LINES

Insulation from supporting structures

o Suspension insulators are used to prevent arcing (current jumping between conductors)

o Ceramic plates are used - good insulators

Porous material

90%air

Protection from lightning strikes

o Shield conductorsare non-current carrying wires placed at the very top

Conducts charges from lightning strikes and earths to ground

Prevents damage to tower, nearby substations and transmission lines

o Towers are widely spaced, in case a tower falls


33/78

Physics

Shaddy Hanna

32 of 77

ASSESS:EFFECTS OF THE DEVELOPMENTS OF AC GENERATOR

SOCIETY

Advantageso Improvements in technology/communication

Led to the parallel development of transformers which have allowed the long-

distance transmission of electricity; beneficial to society

o Improved standards of living

Many tasks performed mechanically, can now be accomplished by electricity

Less labour intensive jobs

Disadvantages

o Development of mass generators have forced the disturbance of many environments home

to humans

o Reliance on electricity; vulnerable to system loss due to electrical failure

ENVIRONMENT

Advantages

o Electricity has replaced older more-polluting tech

Electric trains instead of steam trains

Disadvantages

o Powered by fossil fuels to produce torque

Contributes to greenhouse effect and global warming

o Production of hydro-plants has disturbed tribes of indigenous people land clearing

ASSESSMENT

The advantages on society AC generators have caused and the technological improvements they have

caused outweigh the environmental damage they may have caused


34/78

Physics

Shaddy Hanna

33 of 77

ANALYSE: COMPETITION BETWEEN WESTINGHOUSE (AC) VS EDISON (DC)

EDISON SUPPORTED DC

Invented a meter to allow customers to be billed for energy proportional to consumption Attempted to sabotage transmission of AC

o Published books describing fatal AC incidents using Westinghouse AC generator:

Electrocuting animals in public via public demonstration

Used AC to create the electric chair

o Lobbied against use of AC in state legislatures

Advantages:

o Doesnt cause energy loss through EM induction or radiation

o Worked well over short distances

o Solid state switching allows change from DC -> AC

o DC transmissions requires minimum two conductorsreducing cost

Disadvantages:

o Power loss was too significantcannot be minimized by transformers

WESTINGHOUSE SUPPORTED AC

Advantages:

o Worked efficiently over long distances

Power loss could be made insignificant

Via use of transformers

Transmission lines were made thinner/lighter

o

Economic advantages outweigh the safety concerns Proven by the generation of electricity at Niagara Falls in 1896

Disadvantages:

o Power loss occurs by releasing EM radiation

o Skin effect where AC travels through outer portion of conductor;

Reduces cross-sectional area

Increases resistance; heat loss

o AC transmission requires at-least 3 conductors = higher cost


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Physics

Shaddy Hanna

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TRANSFORMERS

DESCRIBE:THE PURPOSE OF TRANSFORMERS

Transformers are used to change voltage in appliancesso they can function

o When voltage increases, current decreases

Transformers rely on the principle of induction

o Require continual change in EMF

o Therefore, an AC current is used to

produce a continual change of magnetic

flux

DC current only produces a change in EMF

when it is turned on and off.

= = In the primary coil: = In the primary coil: = Thus, since the change in magnetic flux in the primary coil is equal to that in the secondary coil:

= COMPARE:TYPES OF TRANSFORMERS

Step Up(more turns) Step Down (less turns)

> > Higher output voltage Low output voltage

Lower output current Higher output current

Used in power stations to reduce

current for long-distance transmission

Used at substations to reduce

transmission line voltage for

domestic/industrial use

Used in TVs and computer monitors operate cathode ray tubes

Used in computers, radios, CD playersto reduce 240V to lower V.

EXPLAIN:CONSERVATION OF ENERGY IN TRANSFORMERS

Power is defined as the rate of energy utilization, or joules per second.

Energy cannot be created, thus the input power and output power must be conserved

= =

=

=


36/78

Physics

Shaddy Hanna

35 of 77

DISCUSS: HOW HEATING EFFECTS OF EDDY CURRENTS ARE OVERCOME

Due to the large heat eddy currents give off; heat is minimized in the following ways:

o Insulated layers (laminations)in the iron core

Numerous smaller eddy currents form

Give off less heat

Improves transformer efficiencies

o Ferrites - Impure mixtures of iron ores

(substances are bad conductors of heat)

More efficient (cooler) transformer

o Coolant - Does not minimize eddy currents nor efficiency yet it does prevent overheating

EXPLAIN: ROLE OF TANSFORMERS IN AUSTRALIA TRANSMISSION

Substations are used to step down/step up voltage as they are transmitted

o

Since power generated is only at 23 kV, transformers step up voltage to 330 kV

This is optimal for transmission, since it has low current (P=VI)

o At the entrance of cities, substations step down voltage to 33kV and then to 11kV

Pole transformers step down voltage to 415 V (industrial) and 240 V (domestic use)

DISCUSS:USE OF TRANSFORMERS WITH DC APPLIANCES

Mains domestic power supply is 240 V

o Some appliances only require 12-24V

Transformers are used to step downthe voltage.

E.g. laptops, phone chargers

o Some appliances require more than 240 V

Transformers are used to step up the voltage.

E.g. Fridges, Microwaves

DISCUSS: IMPACT OF DEVELOPMENT ON SOCIETY

Advantages:

o Allowed different voltage appliances to exist e.g. toasters, computers etc

o Resulted a National Power Grid

o Spread of population due to increased efficiency of long-distance transmission

Minimising of power loss due when transmitting due to transformers

Disadvantages:

o Increased dependency on electricity

Lack of power supply can compromise safety E.g. Hospitals etc


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Physics

Shaddy Hanna

36 of 77

AC MOTORS

AC SYNCHRONOUS MOTOR

Similar to a DC motor, yet slip rings are used instead of a split-ring commutator External magnetic field is supplied by electromagnets that are connected with coils of armature

DESCRIBE: FEATURES OF AN AC INDUCTION MOTOR

Magnetic Field:produced by 3-phase paired electromagnets

o o AC current of each solenoid is out of phase by 120 degrees

o Therefore, the variation in the magnetic field strength of each electromagnet creates a

virtually rotating" magnetic field

Thus an EMF (and current) is induced on the squirrel cage

Squirrel Cage:a circular arrangement of conductors connected to end rings

o No current is direct supplied to the rotor

o As an EMF is induced in the conductors of the cage, current flows to oppose the change

o A force is experienced by the squirrel cage causing rotation of the cage in direction

Slip Time:measure of the difference in rotational speed of the rotating magnetic field

o Ensures a constant relative motion between conductor and field

Increasing load = increase in slip time

= = = = Advantages

o

No brushes/commutatorless frictional wear, no electrical discharges across gaps

More efficient

Easier to maintain

o Ability to easily control speed (changing frequency)

o Higher power output than normal AC motors

o Not possible to burn out

Due to no back EMF

Disadvantages

o Requires an AC supply, which determines maximum speed (supply frequency)

o More expensive to build


38/78

Physics

Shaddy Hanna

37 of 77

IDEAS TO IMPLEMENTATION

CATHODE RAYS LED TO THE DEVELOPMENT OF TELEVISION

EXPLAIN:THE APPARENT INCONSISTENT BEHAVIOUR OF CATHODE RAYS CAUSED

DEBATE AS TO WHETHER THEY WERE CHARGED PARTICLES O R EM-WAVES

PRAC:DEMONSTRATING PROPERTIES OF CATHODE RAYS USING DISCHARGE TUBES

CATHODE RAYS FITTED THE WAVE MODEL

CONTAINING A MALTESE CROSS

Cathode rays were shone on a solid object.

The shadow produced behind the object suggested that the waves travelled in straight lines

o Suggests that cathode rays obeyed diffraction rays (shadow) bent around the cross

WITH A FLOURESCENT DISPLAY SCREEN

Cathode rays were shone through a phosphorus screen

o Allowed their path to be observed

o Suggested that cathode rays transferred energy

WITH THIN METAL FOILS

Cathode rays were shone through a sheet of thin metal foil

o Cathode rays penetrated through

CATHODE RAYS FITTED THE PARTICLE MODEL

CONTAINING ELECTRIC PLATES/MAGNETIC COILS - DETERMINING THE CHARGE SIGN ON CRS

Cathode rays were shone through an electric field

o The cathode ray was attracted to the positive plate

Cathode rays were shone through a magnetic field

o The cathode rays were deflected accordingly

Suggest that cathode rays were negatively charged particles

CONTAINING A GLASS WHEEL

Cathode rays were shone onto a glass wheel that was free to move

o It was observed that the glass wheel moved

o Suggested that cathode rays had momentum (and mass)


39/78

Physics

Shaddy Hanna

38 of 77

EXPLAIN:CATHODE RAY TUBES ALLOWED THE MANIPULATION OF A STREAM OF

CHARGED PARTICLES DISCHARGE TUBES

Cathode ray tubes were glass tubes (vacuums) containing two electrodes

o

They produced a stream of charged particles through it Emitted from the cathode and collected by the anode

Particles were attracted to the anode due to potential difference

o Cathode rays (charged particles) caused the glass to glow green upon interaction

PRAC:OBSERVE THE OCCURRENCE OF DIFFERENT STRIATION PATTERNS FOR

DIFFERENT PRESSURES IN DISCHARGE TUBES

When electrons collided with gas particles, particles ionised, causing the emission of light

The pressure of the discharge tube affects how cathode rays travel:

At lower pressures, there were less gas particles to collide with, allowing electrons to travel further

without ionising a gas particle through collision

o At normal air pressure nothing is observed inside the tube.

o As the air is evacuated, purple streamers begin to appear that are continuous from the

anode to the cathode.

o Next striations appear, the colour is now dull pink and there is a gap between the cathode

and the first striation.

o The gap increase and the striations become dimmer.

o Eventually no striations are seen anymore, only a green glow on the glass.

Safety Precaution:Induction coil used to generate power for the CRT emits X-rays

o Thus, students should stand at least 3m away from the apparatus


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Physics

Shaddy Hanna

39 of 77

IDENTIFY:MOVING CHARGED PARTICLES IN A MAGNETIC FIELD EXPERIENCE A FORCE

A moving charged particles in a magnetic field will experience a magnetic force

DESCRIBE (QUANTITATIVELY): THE MAGNETIC FORCE ON A CHARGED PARTICLE

=IDENTIFY:CHARGED PLATES PRODUCE AN ELECTRIC FIELD

An electric field is set up by a potential difference between two oppositely charged parallel plates

DESCRIBE (QUANTITATIVELY): ELECTRIC FIELD DUE TO OPPOSITE PARALLEL PLATES

= = Where:

o Potential Difference in Volts (V)

o Distance in Metres (m)

o Electric Field Strength in Volts

per Metre (Vm-1)

= =

Where:

o Force in Newtons (N)

o Charge in Coulombs (C)

o Electric Field Strength in

Newtons per Coulomb (NC-1)

DISCUSS (QUALITATIVELY) :ELECTRIC FIELD STRENGTH DUE TO CHARGED PARTICLES

AND OPPOSITE PARALLEL PLATES

An electric field is any point where a charged particle will experience a force

o Within the field, the force on the particle will be equal no matter where it is

The strength of the

electric field due to a

positive or negative

point chargediminishes

with distance from the

object.

The more linesdrawn

around a given charge,

the stronger the field

The electric field

between two oppositely

charged parallel plates is

uniform in strength and

direction.The field

direction is defined as atright angles to the plates

and away from the

positive plate.


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OUTLINE:J.J THOMSONS EXPERIMENT - CHARGE/MASS RATIO OF AN ELECTRON

Aim:To measure the charge to mass ratio of cathode rays

Equipment:

o Anode: used as a velocity filter (refer to CRT section)

o Tape Measure: to measure the deflection of electrons under different fields

Method:

o Magnets were placed either side of the CRT to produce a uniform magnetic field which

exerted an upward force on the cathode rays measured according to:

=sin =sin90 = o Thompson recognised that the force due to the magnetic field caused the cathode rays to

travel in a circle; thus implying uniform circular motion

= = = =

= o Thomson then balanced out the magnetic field force by that of an electric field until the

cathode ray beam passed through both fields un-deflected (showing that the two forces

were equal)

= = = =

= = 1

= Conclusion: By calculating the charge-to-mass ratio (formula above) of cathode rays, Thompson

concluded that Cathode Rays were in fact particles since they had a charge and mass, now calledelectrons.

Tape Measure


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OUTLINE:MAIN FEATURES IN CRT OF CONVENTIONAL TV D ISPLAYS & OSCILLOSCOPES

ELECTRODES IN THE ELECTRON GUN

Cathode: source of electronso Supplied with very high voltagereleased electrons by thermionic emission

o Electrons are accelerated to the anode (due to their attraction and high diff. in potential)

Anode:filters out slow electrons and focuses electron beam

o Slow/faster electrons are deflected due to magnetic/electric force imbalances

o Thus they are deflected and a final focus beam of electrons with the same speed are left

THE DEFLECTION PLATES (OR COILS)

Electrons can be made to deflect through the use of an electric plates or magnetic coils

o One set can be used to move the electron in a vertical direction

o The other set can used to direct the path of the electron horizontally

THE FLOURESCENT SCREEN

The glass screen is made up of some fluorescent material.

o Thus when struck by an electron, they give off EMR in the form of visible light

TV DISPLAYS

3 electron guns exist (one for each of the primary colours red, green, blue)

A grid also exists to vary the brightness of a pixel by altering the flow of electrons

Deflection system occurs by the use of exteriorcoils which deflect by magnetic force

Fluorescent screen has three different types of coloured phosphorsfor each corresponding e-gun

o Electrons emit visible light upon interaction with corresponding phosphor

o Shadow mask is placed before the screen to prevent electrons hitting the wrong spot


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OSCILLOSCOPES (CROS)

Displays a signal which allows voltage to be visualised

o Converts an analogue signal into a voltage vs. timegraph

Internaldeflection systemoccurs by the use of a horizontalplates which deflects the electrons

according to a controllable time base and vertical plates which vary according to the voltage signal by

varying the strength of the plates


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THE MODEL OF LIGHT, THE PHOTOELECTRIC EFFECT A ND BLACK BODY RADIATION

OUTLINE: HERTZ EXPERIMENT

RECALL:MAXWELLS THEORY OF ELECTROMAGNETIC WAVES

In 1984, Maxwell showed that light was an electromagnetic disturbance by four equations

o His work unified the field of electricity, magnetism and optics

o It predicted that the EM spectrum consisted of much more than just light

EM waves are a self-propagating electric and magnetic disturbance

Hertz then experimentally showed this by discovering radio waves (the first non-light EM waves)

DESCRIBE: HERTZS OBSERVATIONSOF THE EFFECT OF A RADIO WAVE ON A RECEIVER

Hertzs experiment consisted of three parts

o Primary loop (Transmitter)

The induction coil stepped up the voltage from the power source to provide a great

potential between the spark gap

producing a sparko Secondary loop(Receiver)

Hertz noted that a spark would jump across the gap in the receiving loop when held

near the primary loop

Hertz then altered the distance between both gaps until the frequency of the

secondary loop was in sync with the primary loop (representing a standing wave)

o Parabolic mirrors

Parabolic mirrors were set up around the apparatus using each spark gap as a focus

to channel EMR waves from all directions, back to the secondary loop

Thus making the spark more noticeable for observation.


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DESCRIBE: THE PHOTOELECTRIC EFFECT HERTZ PRODUCED BUT FAILED TO INVESTIGATE

a negatively charged object loses its charge more readily when illuminated by UV light

o Hertz noticed that when UV light was shone on the receiving loop, the spark gap could be

made greater with the same size spark occurring

i.e. the spark seemed greater

OUTLINE: HOW HERTZS SHOWED RADIO WAVES RELATE TO LIGHT WAVES (SPEED C)

Hertz showed that these radio waves behaved like light since they could:

o Reflect, refract, interfere, diffract, be polarized

Hertz also proved that the radio waves travelled at the speed of light, , by the formula: = o The frequency of the waves was known by the use of a LCP

o By altering the distance between the loops, Hertz was able to calculate the wavelength of

the radio waves using theprinciple of interference(getting a standing wave)

PRAC: DEMONSTRATE THE PROUCTION/RECEPTION OF RADIO WAVES

When an induction coil was set up and placed beside an AM radio tuned on a cannel that had no

broadcast, the radio gave of lots of static, proving that radio waves were in fact being produced


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QUANTAM THEORY

RECALL: BLACK BODY RADIATION

A black body is a theoretical object that is able to perfectly absorb and emit EMR at all frequencieso Therefore; black body radiation is the radiation black bodies emit

UV CATASTROPHE

Classical theory could not explain two characteristics of the nature of black body radiation curves:

1. Assumed the hotter an object , the more energy released, the greater the intensity of

radiation Violating the principle of Conservation of Energy

2.

Was unable to explain the peak in curves as the wavelength decreased

IDENTIFY: PLANCKS HYPOTHESIS QUANTUM THEORY

Energy occurred in discretepacketshe called quanta

o Disproving the previous theory that energy was continuous

These discrete levels of energy also increased at integer multiples of a single base unit

o Plancks constant, = 6 . 6 2 6 1 0 Plancks hypothesis derived a new black body law to explain the curves:

o Each quanta is able to interact differently with the black body

o The peak intensity is due to the black body itself being able to interact most optimally with a

specific wavelength of energy (changing with temperature)

= :=( 1)


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IDENTIFY:EINSTEINS CONTRIBUTION TO QUANTUM THEORY/BB RADIATION

THE PHOTOELECTRIC EFFECT

The photoelectric effect is the phenomenon whereby electrons are emitted from the surface of amaterial due to the absorption of energy from EMR

Phillip von Lenard was the first to notice and study the photoelectric effect (other than Hertz)

1.

The energy of an electron is dependenton the frequency of the EMR

o However, is independenton the intensity of the EMR2.

The photocurrent is dependenton the intensity of the EMR

The experimental data could not be explained by classical physics, and thus the need for Quantum

theory to explain the observations shown by Einsteins explanation

THE PHOTOELECTRIC EFFECT:EINSTEINS EXPLANATION

Einsteins explanation was based on the Quantum theory to explain the phenomenon:

o He explained that each photon interacted in an elastic collision with an electron on the

surface of a metal

o Consequently, energy and momentum are entirelytransferred from the photon to the

electron

o As a result, an electron will absorb enough energy to be emitted from the surface of the

metal, so long as the photon energy is greater than the work functionof the material

The work function is the energy needed to remove an electron from a material

As a result, Einsteins explanation proved many un-explained aspects of von Lenards studies:

o The max. energy of the electron is only dependent on thefrequencyof the photons

oThe number of electrons emitted (photocurrent) is dependent on the intensity of thephotons, explaining a threshold frequency.

From this explanation, Einstein also predicted

there would be a cut-off frequency (threshold

frequency)where no electrons would be emitted

as a result of the incident photon energy being

too low for the work function

Finally, Einsteins explanation could calculate the kinetic energy of an ejected electron:

ASSESS:EINSTEINS CONTRIBUTION TO QUANTUM THEORY

One of Einsteins greatest contributions to Quantum theory was using Plancks hypothesis (that

energy was quantised) in his explanation of the photoelectric effect to provide explanations to manymathematical concepts which Planck hypothesised yet could not prove, further leading to the

accepted theory of a wave-particle dualityand establishing the particle model of light

For stopping voltage:

=

= = = = 12


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SUMMARISE:THE PHOTOELECTRIC EFFECT IN PHOTOCELLS

A photocellis a device which produced current to flow in the presence of light ( or any other EMR)

o In the presence of EMR, the metal cathode will emit electrons.

o These electrons are then accelerated towards the anode and a complete circuit is produced.

o

If the light beam stops (i.e. if the EMR is blocked by a solid object), the current stops

EXPLAIN:THE PARTICLE MODEL OF LIGHT

The particle model of light stated that all EMR (including light) travels in photons (packets of energy)

o Photons are a massless particle (no rest mass) and thus can travel at speed o Explained how waves could have momentum wave-particle duality

o The model claimed that a photons energy is directly proportional to the frequency of the

radiation, according to Plancks formula:

=

DISCUSS:DIFFERING POLITICAL VIEWS OF EINSTEIN AND PLANCK

Einsteinwas a German-born Jew

o He remained a pacifist during WWI. It may seem that he put these views aside when Hitler

came into play due to his letter to the USA president to build the atomic bomb; however that

was a direct response to the fear that the Germans would build it first, causing more

detrimental damage to society. It is important to note, however, that after Hitler was

deposed, Einstein wrote another letter to USA to never use the atomic bomb, EVER.

o He believed that the political and social barriers to scientific research should be removed

since scientific research/experimentation was integral to the development of scientifictheory which would one day benefit society.

o Government and science must be separated

o Government should not push their political agenda on society

Planckwas a nationalist, a proud German

o Supported the use of science for political and social gain as it benefited society.

o However, he did not support the war and the persecution of Jews, rather continued to teach

Einsteins theories.

o Government and science must be together


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SEMICONDUCTORS

IDENTIFY:ELECTRONS IN SOLIDS ARE SHARED BETWEEN ATOMS AND MOVE FREELY

In metallic solids, a crystal lattice of positive metal ions are bonded together (covalently) Valence electrons are delocalised and shared between the atoms to move freely

o For this reason they conduct electricity

DESCRIBE: DIFFERENCE BETWEEN CONDUCTORS, INSULATORS, SEMICONDUCTORS

BAND STRUCTURE

TheExclusion Principle:No two electrons in a system can occupy the exact same energy level

o Furthermore, the larger the system, the greater the width of the band

Valence band:the outermost shell of electrons which are determine the reactivity of a substance Conduction band:the band where electrons are able to move freely and hence conduct electricity

RELATIVE ELECTRICAL RESISTANCE

Insulators:the conduction band and full valence band is separated by a large forbidden energy band

o This gives the material a high electrical resistance since it requires energy to force valence

electrons to move into the conduction band

Conductors:the conduction band and valence band overlaps allowing valence electrons to easily

move into the conduction band

o This gives the material a low electrical resistance since no energy is needed to conduct

Semiconductors:conduction band and valence band are separated by a small forbidden energy band

o

With enough energy (often thermal energy), valence electrons can be excited to move upinto the conduction band.

o Thus, electrical resistance decrease as thermal energy increases and more valence electrons

are forced into the conduction band.


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COMPARE:RELATIVE NUMBER ELECTRONS THAT CAN DRIFT BETWEEN ATOMS

IDENTIFY:ELECTRON-HOLE PAIRS

When an electron leaves the valence band (by moving to a different atom or being excited into the

conduction band, it leaves a hole

o A holeis the absence of an electron.

Holesact as a positiveflow of current in the valence bandmoving towards the negative potential

Electronsact as a negativeflow of current in the conduction bandmoving towards the positivepotential.

NOTE: The speed of the electron-current flowing through overlapping conduction bands is much

greater than the hole-current moving from atom to atom.

PRAC: ELECTRON-HOLE PAIR D EMONSTRATION

To model the electron-hole behaviour in semiconductors we take:

o studentsas electrons; and

o chairsas holes

When a hole is created, this can be represented as an empty chair amongst students sitting on chairs

o

The electrons (students) will move into the hole, leaving a hole in their current seats

o As a result, neighbouring electrons (students) will then move that hole until the hole is at the

end of the chain

IDENTIFY:THE USE OF GERMANIUM IN EARLY TRANSISTORS (SEMICONDUCTORS)

Germanium was widely used as a semiconductor in early transistors since it was easier to extract and

purify, despite being relatively scarce

Silicon is more difficult to purify, however it is very abundantmaking it relatively cheap to extract

o Retains semi-conducting properties at higher temp, allowing higher electric currents

oForms a silicon dioxide layer than can be doped, made into thin layers, and acts as a coatedinsulator for the conducting silicon inside


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DESCRIBE:DOPING A SEMICONDUCTOR CAN CHANGE ITS ELECTRICAL PROPERTIES

Doping involves the addition of a tiny amount (up to 1ppm) of an impurity atom (having a different

valence level) added to pure crystal structure to alter its electrical properties

o Thus allowing for extra energy bands to exist between the energy gap, reducing the energy

required to excite electrons into the conduction band and thus electrical resistance

INTRINSIC SEMICONDUCTORS

Semiconducting properties of a material (such as silicon) will occur naturally without doping

o However, some form of thermal energy is necessary to excite valence electrons into the

conduction band

EXTRINSIC SEMICONDUCTORS

Semiconducting properties of a material are modified by the addition of a

dopant atom allowing them to conduct in room temperature

o An element is chosen with one more or one less valence electron

then the atoms of the original material

IDENTIFY: DIFFERENCES BETWEEN P-TYPEAND N-TYPESEMICONDUCTORS

P-TYPE SEMICONDUCTORS

The dopant is a group 3 atomgallium(or boron, aluminium)

As a result, there is a hole in the crystal structure Under the influence of an electric field, electrons will move into

the hole, consequently creating new holes in adjacent atoms

o Therefore, alongside other electron-hole pairs, there is

an excess of positive holes as charge carriers over electrons

These extra holes allow the conduction band to accept electrons with less energy lowering the

acceptor levelof the conduction band reducing the energy gap between the bands

N-TYPE SEMICONDUCTORS

The dopant is a group 5 atomphosphorus(or arsenic)

Since there is one extra electron, it is forced into the conduction

band

o Therefore, alongside other electron-hole pairs, there is an electrons

as charge carriers over positive holes

These extra electrons allow the valence band to donate electrons with less energy rising the donor

levelof the conduction band reducing the energy gap between the bands

P-type N-typeConduction band

Valence band


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DESCRIBE: DIFFERENCES BETWEEN SOLID STATE DEVICES AND THERMIONIC DEVICES

THERMIONICDEVICES

Thermionic devices use thermal electron emissionin order to perform various tasks by altering andcontrolling the flow of current

Diode:involved a thermionic device of only two electrodes in a evacuated glass tube

o Cathode: coated in a metal which easily produces thermionic electrons

When heated sufficiently, electrons are emitted from the surface and travel towards

the anode

o Anode:metal which does not easily produce thermionic electrons

o If we attempt to reverse the cathode/anode polarity, no thermionic electrons are produced

and the device is a diode thus acting as a switch

Diodes allowed only unidirectional conduction: useful for converting ACDC

Triode:involved a thermionic device of multiple electrodes

o A third electrode was added: the grid

When a voltage is placed on the grid (i.e. from a microphone), the flow of electrons

can be controlled and varied

Small changes of the grid voltage cause large changes to the main electron current

passing through the valve, i.e. small changes are amplified

If the grid voltage is large enough, it can also block the main current i.e. acting like a

switch

o Triodes were useful for use as a current amplifieror switch
http://www.statemaster.com/encyclopedia/Image:Triode-vacuum-tube.pnghttp://www.statemaster.com/encyclopedia/Image:Diode-vacuum-tube.png


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SOLID STATE DEVICES

Solid state devices use semiconductors to perform their tasks

P-N JUNCTION (DIODE)

A junction between the p-type and n-type semiconductor

Only needs to be a few atom layers thick

At the junction:o Electrons cross and fill the holes near the junction, creating apotential differenceacross it

An equilibrium is eventually reached

o Since there are now no charge carriers left near the junction, it is an insulator layer

Forward Bias

o Conventional current flows into the p-type (electrons flow into the n-type)

e will flood the n-type semi-conductor with excess electrons

Thus, e fill most of the holes near the junction narrowing the depletion zone.

o Furthermore, since the depletion zone (insulator layer) has been narrowed, current now

flows across the junction

Reverse Bias

o Conventional current flows into the n-type (electrons flow into the p-type)

e are dragged out of the n-type, decreasing the amount of mobile charges

Thus, widening the depletion zone.

o Furthermore, since the depletion zone (insulator layer) has been widened, current is now

obstructed from flowing across the junction

-+

+-


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DISCUSS:WHY SOLID S TATE DEVICES REPLACED THERMIONIC DEVICES

Thermionic Devices Solid State Devices

Documents

Physics Notes by Shaddy Hanna