9702 Physics - Definitions and Statements v1.0

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Dr. Lee Chong Yew v1.0

Definitions and Statements for CIE Physics This document contains factual information useful for quick recalls for As level physics. It is not intended for introducing physical concepts already covered in textbooks, and it does not contain mathematical equations or formulas.

Though definitions and statements on physical quantities/concepts can be found in recommended texts, they are worded differently and may vary in detail. These discrepancies are potentially confusing, and the confusion is compounded by exam mark schemes offering yet another set of definitions that are worded differently. It must be noted however that definitions listed in the textbooks and mark schemes ultimately bring about the same meaning. The difference is only in the choice of words used and the depth of detail offered.

As such, every effort was taken to extract definitions and statements from past exam papers.

This was done to ensure conformity with answers finalized by chief examiners from the UK. Only the best answers from past year papers are listed (best to my ability anyway). I may reinforce answers with details from textbooks when required. Legend

• Blue – taken from past exam papers / already listed in the syllabus

• Green – taken from the “International A/As level physics” textbook

• Orange – taken from the “Physics coursebook” textbook

• Red – comments by Dr. Lee Chong Yew

M Method – M-type marks are given when correct physical concepts are stated

A Accuracy – A-type marks are awarded when accurate implications/facts/observations are stated. For example, in explaining elastic extension of a wire, students can write:

1. Object returns to original length (M – type mark)

2. When force is removed (A – type mark)

If you get the M-type mark wrong in this example, the A-type mark will not be awarded.

C Compensatory – marks awarded to candidates for providing numerical answers correctly even when the formula is not listed.

B Independent – these marks are self-contained marks given for each correct statement. They do not rely on M-type marks to be correct.

* Not stated explicitly in the syllabus but included for better coverage

Notes:

1) Marks: It turns out that ½ mark do exist (2013 exam mark schemes). Be precise to prevent ½ mark

deductions.

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Acknowledgements

My special thanks to the following students who have volunteered their time to map pass

exam questions to the syllabus. Your work contributed greatly to the creation of this document =)

Dr. Lee Chong Yew

11th November 2013

Month Paper 2013 2012 2011 2010 2009 2008

June 11Wei-En Dr. Lee

12

13

21Dr. Lee

22

23

November 11Chew Shyang

12

13

21Gary Liew

22

23

Chew Hou

Gary Liew

Yagi Makoto

Le Ee

Ju Vi

Chia Ling

Emily Wong

Chew Shyang (1)

Gary Liew

Jin Wei (1)

Melissa Phon

Zhi Liang

Zhi Liang

Melissa Phon

Emily Wong

Han Khai (1)

Yagi Makoto

Angeline Shak

Archishaa

Yi Chern

Terry

Hooi Shin

Adrian

Shang Herng

Ethan Ong

Joshua Ng

Chuen Ken

Justin Lee

Jo-Ee

Lerinna

Timothy Chin

Angeline Hong

Jamie Cham

Chin Yoong

Shankar

Yi Xie

Sarika

Coreen Soh

Jeremy Ng

Student Assigned

Yew Jung

Mao Jian

Benjamin Lee

Sarah Hiew

Yew Jung

Janice Wu

Joelle Teoh

Chong Jun

Jin Wei

Joanna Grace

Jonathan Choy

Yvonne Low

Yung Sun

Chun Yang

Kirjon

Han Khai

Adrian Yap

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Exam Tips

1) Many essay type questions in P2 are recycled time and again (especially on waves and nuclear

physics). They can therefore be answered using a general set of statements. But how do you

identify these general statements?

a) First, you must get your physics right by including a physical concept that is applicable to the

question (you rarely have more than 1 concept per question).

b) How then do you identify these concepts? Easy, look for marks allocated [M1] in the mark

schemes. This is the method mark AKA the main idea mark. If you get the main idea wrong,

you won’t score any mark for that particular section.

c) You will soon realize the [M1] (main idea) mark is fairly similar for many question.

d) Once the main idea is established, you should proceed to write down the

implications/observations based on the physical concept. These are the [A1] type marks.

2) There are MANY instances where students are required to devise an experiment to observe OR

verify physical phenomena/constants. These questions are fairly straightforward, and can be

attempted by adhering to the following steps:

a) List down all the apparatus you need

b) Explain how each apparatus is used to obtain measurements

c) Compute/Analyze your data or provide suitable conclusion based on your observation.

d) List also precautions taken to ensure measurement is not distorted by systematic error (e.g.,

apparatus calibrated, no zero error) and random error (e.g., repeat measurement and obtain

average value)

3) Never enter the exam hall with an empty stomach and make sure you are well rested prior

exam.

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Section I: General Physics

1 Physics quantities and units

(a)

(c)

show an understanding that all physical quantities consist of a numerical magnitude and a unit

express derived units as products or quotients of the SI base units and use the named units listed in this syllabus as appropriate

Quantity Symbol Unit Derived unit

displacement s, x - m

Force F N kg.m.s-2

Young modulus E Pa kg.m-1s-2

The difference between each column on table above must be noted (e.g., what is a physical quantity, or what a derived unit is).

Derived units consist of some combination of the base units. The base units may be multiplied together or divided by one another, but never added or subtracted.

(b) recall the following SI base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K)

SI units is founded upon seven fundamental or base units.

Comment: You must memorize all of the SI base units above. All other units are derived units (e.g., volt, pressure, force etc). Don’t be confused.

(d) use SI base units to check the homogeneity of physical equations

Homogeneous equation: In any equation where each term has the same base units, the equation is said to be homogeneous or ‘balanced’.

(f) use the following prefixes and their symbols to indicate decimal submultiples or multiples of both base and derived units: pico (p), nano (n), micro (µ), milli (m), centi (c), deci (d), kilo (k), mega (M), giga (G), tera (T)

Prefix Symbol Multiplying factor

Prefix Symbol Multiplying factor

peta P 1015 centi c 10-2

tera T 1012 milli m 10-3

giga G 109 micro μ 10-6

mega M 106 nano n 10-9

kilo k 103 pico p 10-12

deci d 10-1

Sometimes it is useful to estimate how big the number is. This process is called determining the order of magnitude (the power of ten a number is raised). For example, 1.2 x 105 x (2.6 x 106) ≈ 1011. If the answer has a different order of magnitude, say, 1012 we know that it is wrong

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(j) distinguish between scalar quantities

Scalar has magnitude/size – B1 (2011/Nov-P23/Q1a)

vector quantities and give examples of each

Vector has magnitude/size and direction – B1 (2011/Nov-P23/Q1a)

(k) add and subtract coplanar vectors

1. The sum of vectors (be it addition or subtraction) is known as the resultant vector.

2. The resultant can be found using a scale drawing of the vector diagram OR by calculation.

3. Only vectors occupying up to two dimensions are covered in CIE. Thus all addition or subtraction of vectors must be on the same plane. Vectors on the same plane are known as coplanar vectors.

(l) represent a vector as two perpendicular components.

1. A single vector can be split up, or resolved, into two vectors. The resolved parts are known as components.

2. In general, a vector is resolved into two components at right-angles to each other.

2 Measurement techniques

(a) Candidates should be able to use techniques for the measurement of length, volume, angle, mass, time, temperature and electrical quantities appropriate to the ranges of magnitude implied by the relevant parts of the syllabus.

Quantity Equipment

Length Meter rule, vernier caliper, micrometer screw gauge

Mass Top-pan balance, spring balance, lever balance

Angle Protractor

Time Stop watch, stop clock, digital timer, c.r.o

Temperature Mercury in glass thermometer, thermocouple thermometer

Current Ammeter (digital or analogue), multimeter

Voltage Voltmeter (digital or analogue), multimeter

Frequency c.r.o

1. A loudspeaker produces a sound wave of constant frequency. Outline how a cathode-ray oscilloscope (c.r.o.) may be used to determine this frequency (2010/Nov-P23/Q3).

a) connect microphone / (terminals of) loudspeaker to Y-plates of c.r.o. – B1

b) adjust c.r.o. to produce steady wave of 1 (or 2) cycles / wavelengths on screen – B1

c) measure length of cycle / wavelength λ and note time-base b – B1

d) frequency = 1 / λb – B1

Watch this video for more info: http://www.youtube.com/watch?v=SxZWcku_Sw0

http://www.youtube.com/watch?v=SxZWcku_Sw0

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(d) show an understanding of the distinction between systematic errors (including zero errors) and random errors

1. Systematic error

a) Will result in all readings being either above or below the accepted value OR the average / peak is not the true value / the readings are not centred around the true value – B1 (2011/Jun-P23/Q1bi)

b) Cannot be eliminated by repeated readings and averaging

c) Can only be reduced by improving experimental techniques (e.g., calibrate devices before use, make sure no parallax error etc).

2. Examples of systematic errors:

a) Zero error – Scale reading not zero before measurements are taken. Check for zero error before measurements.

b) Wrongly calibrated scale

c) Reaction time of experimenter – Delay between the experimenter observing the event and starting the timing device. May be as long as 0.2 – 0.5s.

3. Random errors

a) Results in readings being scattered around the accepted/true value OR readings have positive and negative values around the peak value / values are scattered / wide range – B1 (2011/Jun-P23/Q1bi)

b) Can be reduced by repeating a reading and averaging OR

c) by plotting a graph and drawing a best-fit line.

4. Examples of random errors:

a) Incorrect reading of a scale

b) Inaccurate timing of a complete oscillation

c) Taking readings that changes with time, especially when two instruments have to be read simultaneously.

d) Parallax error

5. State how the instrument is (2010/Jun-P22/Q1bi):

a) checked so as to avoid systematic error in the measurements - look/check for zero error – B1

b) used so as to reduce random errors - take several readings – M1 - to get an average value for the reading – A1

(e) show an understanding of the distinction between precision and accuracy

1. Accuracy is concerned with how close a reading is to its true value

2. Precision is the smallest change in value that can be measured by an instrument or an operator.

3. A precise instrument is one that produces similar values when measurements are repeated.

4. From (2011/Jun-P23/Q1bii): a) When readings are accurate, the peak / average value moves towards the true value

– B1 b) When readings are precise, the scatter between each data is relatively small/ lines

are closer together / sharper peak – B1

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(f) assess the uncertainty in a derived quantity by simple addition of actual, fractional or percentage uncertainties

1. Uncertainty indicates the range of value within which a measurement is likely to lie.

Section II: Newtonian Mechanics

3 Kinematics

(a) define displacement, speed, velocity and acceleration

1. Distance (scalar) is the actual path travelled – B1 (2011/Jun-P22/Q1ciii)

2. Displacement (vector) is the straight line distance between start and finish points (in that direction) / minimum distance– B1 (2011/Jun-P22/Q1ciii)

3. Speed (scalar) = distance/time taken

4. Velocity (vector) = displacement/time taken

5. Acceleration (vector) = rate of change of velocity – A1 (2013/Jun-P23/Q2aii)

(h) recall that the weight of a body is equal to the product of its mass and the acceleration of free fall

(i) describe an experiment to determine the acceleration of free fall using a falling body

The setup

a) Steel ball-bearing held by an

electromagnet

b) An electronic timer

c) A trapdoor/force sensor

The timer activates when the ball is released by the electromagnet, and stops when the ball hits the trapdoor/ force sensor.

Measurements

a) Record the time taken t for ball to drop at height h. b) Repeat the experiment several times for different values of h. c) Plot the graph of h vs t2 d) Good physics: the average time should be taken for each h to reduce random errors.

Data analysis to obtain free fall acceleration

a) Obtain the gradient of the graph b) The gradient = ½ g c) Free fall acceleration = gradient x 2

Sources of uncertainties

a) Electromagnet may retain some magnetic fields when turned off, delaying the complete release of the ball (systematic error)

b) Measuring height h may be subjected to precision error of 1 mm when measured using a meter rule/tape.

(Please see pg. 29 for other configurations)

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(j) describe qualitatively the motion of bodies falling in a uniform gravitational field with air resistance

1. The variation with time t of vertical speed v of a parachutist falling from an aircraft is shown in the figure below (2012/Nov-P21/Q1bii):

Explain the variation of the resultant force acting on the parachutist from t = 0 (point A) to t = 15 s (point C):

a) resultant force = weight – frictional force – B1

b) frictional force increases with speed – B1

c) at start frictional force = 0 / at end weight = frictional force – B1

d) When resultant force is zero on the vertical direction, terminal velocity is reached.

2. A sky-diver jumps from a high-altitude balloon. Explain briefly (2009/Nov-P21/Q2a):

(a) why the acceleration of the sky-diver decreases with time

- (air) resistance increases with speed – M1 - resultant / accelerating force decreases – A1

(b) why the free-fall acceleration is 9.8 ms–2 at the start of the jump.

- (air) resistance is zero OR weight / gravitational force is only force – B1

(k) describe and explain motion due to a uniform velocity in one direction and a uniform acceleration in a perpendicular direction.

Description

1. known as projectile motion.

2. applicable to objects moving at constant velocity, whilst acted upon by a force with vector perpendicular to its velocity.

3. The force could be imparted by gravitational fields (e.g., golfball travelling in the air), or electric field (e.g., electrons moving between parallel plates with uniform electric fields.)

Assumptions

4. Zero frictional forces (e.g., no air resistance)

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Motion

5. Horizontal axis OR axis with constant velocity: a) Acceleration is zero b) Displacement x after time t is x = xo + uxt

6. Vertical axis OR axis where force is acting: a) Continuously acted upon by a constant force b) The velocity v after time t is v = u + at c) The displacement y after time t is given as y = yo + ut + ½ at2

7. The resultant velocity is computed by adding vx and vy

8. The trajectory of the object will result in a parabola

4 Dynamics

(a) state Newton’s 1st law of motion

A body continues at rest or constant velocity unless acted on by a resultant (external) force – B1 (2012/Jun-P22/Q3a)

state Newton’s 2nd law of motion

(resultant) force = rate of change of momentum – B1 (2012/Nov-P22/Q2a)

state Newton’s 3rd law of motion

1. Stated as (2010/Jun-P22/Q3aii): a) force on body A is equal in magnitude to force on body B (from A) – M1 b) forces are in opposite directions – A1 c) forces are of the same kind – A1

2. For the collision between a ball and a wall, state how Newton’s third law apply (2012/Nov-P22/Q2ci):

a) force on the wall from the ball is equal to the force on ball from the wall – M1 b) but in the opposite direction – A1

(b) show an understanding that mass is the property of a body that resists change in motion

(c) describe and use the concept of weight as the effect of a gravitational field on a mass

Weight is the force due to the gravitational field – B1 (2013/Jun-P21/Q2a)

(d) define linear momentum as the product of mass and velocity

(e) define force as rate of change of momentum

(g) state the principle of conservation of momentum

1. Stated as (2013/Jun-P23/Q3ai)

a) the total momentum of (an isolated) system (of interacting bodies) remains constant – M1

b) provided there are no resultant external forces– A1

2. For the collision between a ball and a wall, state how the law of conservation of momentum apply (2012/Nov-P22/Q2ci):

a) change of momentum of ball and wall is zero – B1

(i) recognize that, for a perfectly elastic collision, the relative speed of approach is equal to the relative speed of separation

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1. For air molecules undergoing elastic collision (2013/Jun-P21/Q4c)

a) elastic collision (occurs) when kinetic energy (is) conserved – B1 b) temperature constant for gas – B1

(j) show an understanding that, while momentum of a system is always conserved in interactions between bodies (both elastic and inelastic), some change in kinetic energy usually takes place.

1. In stating the difference between elastic and inelastic collision (2013/Jun-P23/Q3aii)

a) elastic: total kinetic energy is conserved, inelastic: loss of kinetic energy – B1 [allow elastic: relative speed of approach equals relative speed of separation]

2. In describing, realistically, the collision of a ball on the ground (2012/Jun-P21/Q2c): a) kinetic energy of the ball is not conserved on impact – B1 b) speed before impact is not equal to speed after hence inelastic – B1

5 Forces

(a) describe the forces on mass and charge in uniform gravitational and electric fields, as appropriate

(b) show an understanding of the origin of the upthrust acting on a body in a fluid

Upthrust is the pressure difference between the pressure at the bottom of the object and the pressure at the top of the object immerse in a fluid.

(c) show a qualitative understanding of frictional forces and viscous forces including air resistance

1. In describing the motion of a cyclist (2012/Nov-P23/Q3bi): a) as the speed increases drag / air resistance increases – B1 b) resultant force reduces hence acceleration is less – B1 c) constant speed when resultant force is zero – B1 (allow one mark for speed

increases and acceleration decreases)

(e) show an understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity

1. CoG defined as: (2013-22/6-3a) a) the point where (all) the weight (of the body) – M1 b) is considered / seems to act – A1

2. In an experiment used to find the centre of gravity (2010/Nov-P22/Q3c):

(i) List the two forces, other than its weight and air resistance, that act on the card

during the time that it is swinging. State where the forces act.

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a) reaction / upwards / supporting / normal reaction force – M1

b) friction – M1

c) force(s) at the rod – A1

(ii) By reference to the completed diagram above, state the position in which the card comes to rest. Explain why the card comes to rest in this position.

a) comes to rest with (line of action of) weight acting through rod allow CoG vertically below the rod – B1

b) so that weight does not have a moment about the pivot / rod – B1

(f) show an understanding that a couple is a pair of forces that tends to produce rotation only

(g) define the moment of a force and the torque of a couple

1. State the principle of moments (2013/Jun-P22/Q3bii)

The sum of the clockwise moments about a point equals the sum of the anticlockwise moments (about the same point) – B1

2. moment of a force product of the force and the perpendicular distance (to the pivot) (2011/Jun-P21/Q3b)

3. The torque of a couple is the product of one of the forces and the (perpendicular) distance between forces – M1 & A1

(h) show an understanding that, when there is no resultant force and no resultant torque, a system is in equilibrium.

1. In addition, in certain systems are in equilibrium when the net / resultant moment is zero OR sum of clockwise moments = sum of anticlockwise moments (2011/Jun-21/Q3ci)

2. Three co-planar forces act on a body that is in equilibrium. State how the triangle confirms that the forces are in equilibrium (2010/Jun-P23/Q2bii):

- if the triangle is ‘closed’ (then the forces are in equilibrium) – B1

3. Describe how to draw a vector triangle to represent these forces (2010/Jun-P23/Q2bi): a) each force is represented by the side of a triangle/by an arrow – M1 b) in magnitude and direction – A1 c) arrows joined, head to tail – B1

6 Work, energy and power

(a) give examples of energy in different forms, its conversion and conservation,

1. For an object in freefall with air resistance (2013/Jun-P21/Q3a) a) loss in potential energy due to decrease in height (as P.E. = mgh) – B1 b) gain in kinetic energy due to increase in speed (as K.E. = ½ mv2) – B1 c) increase in thermal energy due to work done against air resistance – B1 d) loss in P.E. equals gain in K.E. and thermal energy – B1

2. For the transformation of energy inside a battery and a resistor in a closed circuit (2013/Jun-P21/Q6a) a) Battery – chemical to electrical – B1 b) Resistor – electrical to thermal / heat or heat and light – B1

3. For energy conversions that take place as mass oscillates on a spring (2012/Nov-P22/Q6d):

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a) elastic potential energy / strain energy to kinetic energy and gravitational potential energy

State the principle of conservation of energy

Energy cannot be created or destroyed. It can only be converted from one form to another

(b) show an understanding of the concept of work in terms of the product of a force and displacement in the direction of the force

(f) distinguish between gravitational potential energy, and

From (2011/Jun-P21/Q4a):

a) gravitational potential energy (stored) when mass moved – B1 b) due to work done in gravitational field – B1

electric potential energy, and

From (2011/Jun-P21/Q4a):

a) electrical potential energy (stored) when charge moved – B1 b) due to work done in electric field – B1

elastic potential energy

1. Explain what is meant by strain energy(elastic potential energy) (2009/Nov-P22/Q4a): a) ability to do work – B1 b) as a result of a change of shape of an object/stretched etc – B1

(j) show an understanding of the concept of internal energy

Internal energy is the sum of the total potential energies and the kinetic energies of all the molecules or the solid/liquid/gas.

(k) recall and understand that the efficiency of a system is the ratio of useful work done by the system to the total energy input

1. On why certain systems are not 100% efficient (2013l/Jun-P22/Q1aiii)

a) Name the specific type of energy relevant to the question (e.g., kinetic energy) and mention that is not fully converted as it is exchanged between two objects (e.g., kinetic energy of wind not fully converted to the kinetic energy of blades on wind generators)

b) State why item (a) is true: e.g., heat produced, mechanical friction in bearings. (You must mention specifically where and why loss occurred)

(m) define power as work done per unit time and

derive power as the product of force and velocity

Section III: Matter

9 Phases of matter

(a) define the term density

density = mass/volume (2011/Nov-P21/Q1a)

(b) relate the difference in the structures and densities of solids, liquids and gases to simple ideas of the spacing, ordering and motion of molecules

1. Spacing: how far apart are the atoms on average

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2. Ordering: are they arranged in an orderly manner (crystalline) or in a random way (amorphous).

3. Motion: are they moving quickly, slowly or not at all.

4. How the difference in the densities of solids, liquids and gases may be related to the spacing of their molecules. (2011-23/6-7a)

a) density of liquids and solids similar – B1

b) as spacing in solids and liquids about the same – B1

c) density in gases much less as spacing in gases much greater – B1

d) the spacing of molecules in gas roughly 10 times greater than spacing of molecules in liquids (2010/Jun-P23/Q4ai) – B1

e) volume occupied by gas is 1000 times larger than volume occupied by the same amount of matter in solid/liquid

f) 99.9% of the volume of a gas is empty space

5. Liquid nitrogen has a density of 810 kg m–3. The density of nitrogen gas at room temperature and pressure is approximately 1.2 kg m–3. Suggest how these densities relate to the spacing of nitrogen molecules in the liquid and in the gaseous states. a) spacing (much) greater in gases than in liquids – M1 b) ratio of spacing is about 8.8 – A1

6. The change ∆V in the volume V of some water when the pressure on the water increases by ∆p is given by the expression:

In many applications, water is assumed to be incompressible. By reference to the expression above, justify this assumption (2008/Jun-Q4b):

a) unless ∆p is very large – M1 b) ∆V/Vis very small, (so ‘incompressible’) – A1

(c) describe a simple kinetic model for solids, liquids and gases

1. General assumptions of the simple kinetic model: a) Matter is made up of many tiny particles – atoms or molecules

b) These particles tend to move about (hence kinetic)

c) In solids, atoms are held together by strong interatomic forces, thus they are movement are restricted to oscillations about their equilibrium positions.

d) Work must be done to break the rigid interatomic forces of solid to form liquid so they can move freely.

2. Assumptions of the simple kinetic model of a gas (2011/Jun-P21/Q6a): a) large number of molecules / atoms / particles – B1 b) molecules in random motion – B1 c) no intermolecular forces – B1 d) elastic collisions – B1 e) time of collisions much less than time between collisions – B1 f) volume of molecules much less than volume of containing vessel– B1

3. State the evidence for the assumption that (2010/Jun-P23/Q4ai): a) there are significant forces of attraction between molecules in the solid state:

- solid has fixed volume and fixed shape/incompressible – B1

b) the forces of attraction between molecules in a gas are negligible.

- gas fills any space into which it is put – B1

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(d) describe an experiment that demonstrates Brownian motion and appreciate the evidence

for the movement of molecules provided by such an experiment

1. Explain what is meant by Brownian motion (2008/Nov-P21/Q5a):

a) haphazard / random / erratic / zig-zag movement – M1 b) of (smoke) particles (do not allow molecules / atoms) – A1

2. Suggest and explain why Brownian motion provides evidence for the movement of molecules as assumed in the kinetic theory of gases (2008/Nov-P21/Q5b):

a) motion is due to unequal / unbalanced collision rates(on different faces) – B1 b) (unequal collision rate due to) random motion of (gas) molecules / atoms – B1

3. Smoke from a poorly maintained engine contains large particles of soot. Suggest why the Brownian motion of such large particles is undetectable (2008/Nov-P21/Q5b):

a) collisions with air molecules average out – M1 b) this prevents haphazard motion – A1 c) particle is more massive / heavier / has large inertia – M1 d) collisions cause only small movements / accelerations – A1

4. On describing the apparatus (2013/Jun-P22/Q4a) a) cell with particles e.g. smoke (container must be closed) – B1 b) diagram showing suitable arrangement with light illumination and microscope – B1

5. On observations made from experiment (2013/Jun-P22/Q4b) a) specks / flashes of light – M1 b) in random motion – A1

6. On conclusions about the properties of molecules of a gas (2013/Jun-P22/Q4c) a) cannot see what is causing smoke to move hence (air) molecules smaller than

smoke particles – B1 b) continuous motion of smoke particles implies continuous motion of molecules – B1 c) random motion of particles implies random motion of molecules – B1

(e) distinguish between the structure of crystalline and non-crystalline solids with particular reference to metals, polymers and amorphous materials

With regards to atomic arrangements (2010/Nov-P23/Q2):

a) Crystals/Metals: atoms / ions / particles in a regular arrangement / lattice long range order / orderly pattern – B1 AND (lattice) repeats itself – B1

b) Polymers: long chain molecules / chains of monomers – B1 AND some cross-linking between chains / tangled chain – B1

c) Amorphous solids: disordered arrangement of molecules / atoms / particles – B1 AND any ordering is short-range – B1

(f) define the term pressure

pressure = force / area (normal to force) – A1 (2013/Jun-P21/Q4a)

and use the kinetic model to explain the pressure exerted by gases

1. On pressure exerted by gasses (2011/Jun-P21/Q6b)

a) molecules/atoms/particles in (constant) random/haphazard motion – B1 b) molecules have a change in momentum when they collide with the walls – M1 c) molecules exert equal and opposite force on wall – B1 d) pressure is averaging effect of many collisions – B1

2. On why pressure on mountain is less than sea level (2013/Jun-P21/Q3b)

a) molecules collide with object / surface and rebound – B1

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b) molecules have change in momentum hence force acts – B1 c) fewer molecules per unit volume on top of mountain / temperature is less hence

lower speed of molecules – B1 d) hence less pressure – A0

(i) distinguish between the processes of melting, boiling and evaporation.

1. State one similarity between the processes of evaporation and boiling (2009/Nov-P22/Q2ai):

a) (phase) change from liquid to gas / vapour – B1

b) thermal energy required to maintain constant temperature – B1 (do not allow ‘convert water to steam’)

2. State the differences between the processes of evaporation and boiling (2009/Nov-P22/Q2aii): a) evaporation takes place at surface – B1 b) boiling takes place in body of the liquid – B1 c) evaporation occurs at all temperatures – B1 d) boiling occurs at one temperature – B1

3. Boiling occurs at a fixed temperature for a given atmospheric pressure.

10 Deformation of solids

(b) describe the behavior of springs in terms of load, extension, elastic limit, Hooke’s law and the spring constant (i.e. force per unit extension).

1. Hooke’s Law state that extension is proportional to force / load (2012-22/11-6a) *don’t mention that extension is proportional to mass (2012-21/6-3ci)

(c) define and use the terms stress, strain and the Young modulus

1. stress = force / cross-sectional area – B1 (2013-23/6-4ai) 2. strain = extension / original length – B1 (2013-23/6-4aii) 3. E = stress/strain – C1 (2013-23/6-4bi)

(d) describe an experiment to determine the Young modulus of a metal in the form of a wire

From (2011-22/6-4a):

The Setup

a) clamped horizontal wire over pulley or vertical wire attached to ceiling with mass attached – B1

b) details: reference mark on wire with fixed scale alongside – B1

Measurements

a) measure original length of wire to reference mark with metre ruler / tape – B1 b) measure diameter with micrometer / digital calipers – B1 c) measure initial and final reading (for extension) with metre ruler or other suitable scale

– B1 d) measure / record mass or weight used for the extension – B1 e) Marks for good techniques: measure diameter in several places / remove load and

check wire returns to original length / take several readings with different loads – B1

Data analysis to obtain Young Modulus

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a) determine extension from final and initial readings – B1 b) plot a graph of force against extension – B1 c) determine gradient of graph for F/ e – B1 d) calculate area from πd2/ 4 – B1 e) calculate E from E= F l/ e A or gradient × l/ A – B1

(e) distinguish between elastic and plastic deformation of a material

1. Description of wire extending elastically (2013-21/6-1a) a) wire returns to its original length (not shape) – M1 b) when load is removed – A1

2. Characteristics of plastic deformation: (2012-21/11-5a) a) Wire/body object does not return to its original shape / length when load is

removed – B1

(g) demonstrate knowledge of the force-extension graphs for typical ductile, brittle and polymeric materials, including an understanding of ultimate tensile stress.

1. F-x graph for (2012-22/11-3b): a) Metal: straight line or straight line then curving with less positive gradient – B1 b) Polymer: curve with decreasing gradient with steep increasing gradient at end – B1

2. F-x graph for (2011-22/11- 3ei): a) Ductile material: initially force proportional to extension then a large extension for

small change in force – B1 b) Brittle material: force proportional to extension until it breaks – B1

3. Ultimate tensile strength (2011-22/11-3c):

a) UTS is the maximum force / original cross-sectional area – M1 b) wire is able to support / before it breaks – A1

* The phenomena of elastic hysteresis (exhibited by rubber) is illustrated on the stress-strain diagram below. Explain why a rubber band gets warm when it is repeatedly stretched and released using the diagram below (2010/Jun-P22/Q5b).

a) area between lines represents energy/area under curve represents energy – M1 b) when rubber is stretched and then released/two areas are different – A1 c) this energy seen as thermal energy/heating/difference represents energy released

as heat – A1

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Section IV: Oscillations and Waves

15 Waves

(a) describe what is meant by wave motion as illustrated by vibration in ropes, springs and ripple tanks

1. Wave motion is a means of moving energy from one point to another by particles that vibrate in direction parallel (longitudinal wave) or perpendicular (transverse wave) to the direction of energy transfer.

2. All waves exhibit common properties, where they can be reflected, refracted, diffracted, and can interact to produce interference patterns. These properties can be observed on a ripple tank.

3. Reflection: as waves strike a suitable reflective medium, they are reflected at an angle similar to the angle of incidence. There is no change in the wavelength/wave front.

4. Refraction: The change in direction of a wave due to change in speed

5. Diffraction: defined as the spreading of wave into regions where it would not be seen if it moved only in straight line (aka geometric shadow)

(b) show an understanding of and use the terms displacement, amplitude, phase difference, period, frequency, wavelength and speed

1. From (2010-22/11-5ai,ii): a) Displacement: distance (of point on wave) from rest / equilibrium position – B1

a) Amplitude: the maximum displacement of a particle in the wave.

b) Phase difference: the difference in the relative positions of the crests or troughs of two waves of the same frequency expressed in radians or degrees.

c) Period: the time for a particle in the wave to complete one complete cycle

a) Frequency: number of oscillations per unit time (not per second) – B1 (2010/Jun-P23/Q5ai)

b) Wavelength: distance moved by wave energy / wavefront during one cycle of the source or minimum distance between two points with the same phase or between adjacent crests or troughs. OR One wavelength is the distance between two neighboring peaks or two neighboring troughs that are vibrating in-phase.

c) Speed: speed at which energy is transferred / speed of wavefront (2008/Jun-Q5aii)

2. The variation with distance x along a progressive wave of a quantity y, at a particular time, is shown in the diagram below (2009/Nov-P21/Q5b):

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(i) State what the quantity y could represent. - displacement / velocity / acceleration (of particles in the wave) – B1

(ii) Distinguish between the quantity y for a transverse wave - displacement etc. is normal to direction of energy transfer / travel of wave /

propagation of wave (not wave motion) – B1

(iii) Distinguish between the quantity y for a longitudinal wave - displacement etc. along / same direction of energy transfer / travel of wave /

propagation of wave (not wave motion) – B1

3. Illustration of phase difference:

4. When two progressive waves are in phase, they have a phase difference of 0 radians.

5. When two progressive waves are out of phase, they have a phase difference of π radians.

(e) show an understanding that energy is transferred due to a progressive wave

1. State what is meant by a progressive wave (2009/Nov-P21/Q5a): a) transfer / propagation of energy – M1 b) as a result of oscillations / vibrations – A1

(f) recall and use the relationship intensity ∝(amplitude)2

1. The intensity of a wave is the energy passing through unit area per unit time.

(g) compare transverse and longitudinal waves

1. Transverse waves have vibrations that are perpendicular / normal to the direction of energy travel (2011/Nov-P23/Q5a)

2. Longitudinal waves have vibrations that are parallel to the direction of energy travel (2011/Nov-P23/Q5a)

3. Only electromagnetic waves (a transverse wave) can travel through a vacuum / free space (2012/Nov-P23/Q5a)

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(i) show an understanding that polarization is a phenomenon associated with transverse waves.

1. Polarization is characterized by (2012/Nov-P23/Q5c): a) vibrations are in one direction – M1 b) perpendicular to direction of propagation / energy transfer – A1

2. Illustrations for polarizations

(l) state that all electromagnetic waves travel with the same speed in free space

1. The nature of EM waves

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2. Common measurements students must know:

EM Wave Wavelength/m

Radiowaves >106 to 10-1

Microwaves 10-1 to 10-3

Infrared 10-3 to 7 x 10-7

Visible 7 x 10-7 (red) to 4 x 10-7 (violet)

Ultraviolet 4 x 10-7 to 10-8

X-rays 10-8 to 10-13

γ-rays 10-10 to 10-16

16 Superposition

(a) explain and use the principle of superposition in simple applications

1. Explained as: (2012/Jun-P22/Q6a): a) two waves travelling (along the same line) in opposite directions overlap/meet –

M1 b) same frequency / wavelength – A1 c) resultant displacement is the sum of displacements of each wave / produces nodes

and antinodes – B1

(Some question use superposition and interference interchangeably 2011/Jun-P21/Q7a)

(b) show an understanding of experiments that demonstrate stationary waves using microwaves, stretched strings and air columns

1. Standing wave setup and demonstration using microwaves.

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a) List all apparatus in the diagram above, and identify their functions. Wave source (microwave transmitter), reflecting sheet (to reflect wave), microwave probe and meter to detected wave intensity.

b) Observations: Probe will detect alternating regions of high and low intensities as it is moved from the source to the reflecting sheet. These regions are the antinode and node respectively.

c) Analysis/conclusion:

- Node is detected on the surface of reflecting sheet

- Regions with the highest intensities are the antinodes

- Waves travelling towards the reflector and waves that are reflected interfere to form standing wave patterns.

- The distance between two consecutive node is equivalent to ½ λ

- If two nodes are detected between the reflector and the source (one single loop), the wavelength of the microwave is 2L, where L is the distance between the two nodes (fundamental mode).

- If 3 nodes are detected between the source and the reflector (2 loops), then the wavelength is equal to the distance between the first node and the last node (second harmonic)

2. A string stretched between two fixed points P and Q based on the figure below.

A vibrator is attached near end P of the string. End Q is fixed to a wall. The vibrator has a frequency of 50 Hz and causes a transverse wave to travel along the string at a speed of 40ms–1 . Explain how this arrangement may produce a stationary wave on the string. (2013/Jun-P22/Q5aii) a) waves (travel along string and) reflect at wall/fixed end – B1 b) incident and reflected waves interfere/superpose (to form standing wave patterns)

– B1

c) analysis of wavelength is similar to item (1) above

3. The figure below shows an arrangement for producing stationary waves in a tube that is closed at one end (2012/Nov-P22/Q4a):

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Explain how waves from the loudspeaker produce stationary waves in the tube.

a) waves (travels along tube) reflect at closed end / end of tube – B1 b) incident and reflected waves or these two waves are in opposite directions – M1 c) interfere or stationary wave formed if tube length equivalent to λ/ 4, 3λ/ 4, etc. – A1

4. Use the principle of superposition to explain the formation of a stationary wave (2012/Jun-P22/Q6a):

a) two waves travelling (along the same line) in opposite directions overlap/meet – M1 b) same frequency / wavelength – A1 c) resultant displacement is the sum of displacements of each wave / produces nodes

and antinodes – B1

5. Describe an experiment to determine the wavelength of sound in air using stationary waves. Include a diagram of the apparatus in your answer (2012/Jun-P22/Q6b):

a) apparatus: source of wave (speaker) + detector (microphone attached to a c.r.o) + reflection system (wall) – B1

b) adjustment to apparatus to set up standing waves – consecutive nodes and antinodes detected as microphone is moved from the source to the wall – B1

c) measurements made to obtain wavelength (c.r.o) – B1 (the distance between two nodes is equivalent to ½ λ)

(c) explain the formation of a stationary wave using a graphical method, and identify nodes and antinodes

1. The properties of nodes and antinodes (2012/Nov-P22/Q4bi): a) Node: no motion (as node) / zero amplitude – B1

b) Antinode: vibration backwards and forwards / maximum amplitude along length – B1 OR position (along wave) where amplitude of vibration is a maximum – B1 (2008/Jun-Q5bii)

2. On formation of standing waves:

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3. When the waves that form the standing wave (see diagram above) are 90o apart (or separated by a time equivalent to 25% of the period), destructive interference will result. If they are 180o apart, constructive interference will result, but the amplitude will flip to the other end. See the diagram below:

(d) explain the meaning of the term diffraction

1. State what is meant by the diffraction of a wave (2010/Jun-P21/Q4a). a) when a wave (front) passes by/incident on an edge/slit – M1 b) wave bends/spreads (into the geometrical shadow) – A1

2. Describe the diffraction of monochromatic light as it passes through a diffraction grating (2012/Nov-P21/Q4a):

a) waves pass through the elements / gaps / slits in the grating – M1 b) wave bends/spreads (into the geometrical shadow) – A1

(award 0/2 for bending at a boundary) (2008/Nov-Q6a)

The term geometric shadow is not found in textbooks.

(e) show an understanding of experiments that demonstrate diffraction including the diffraction of water waves in a ripple tank with both a wide gap and a narrow gap

1. Use the setup of ripple tank explained in part (g) below.

2. Include narrow and wide gaps/slits/openings for waves to pass and diffract as illustrated below.

3. Note that wavelength remains the same even after diffraction.

4. Diffraction is maximum when the width of the slit is equivalent to the wavelength. Diffraction is reduced when the width of the slit deviates from the wavelength.

4. White light is incident on a diffraction grating, as shown in figure below (2012/Nov-P21/Q4bi):

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The diffraction pattern formed on the screen has white light, called zero order, and coloured spectra in other orders.

(i) Describe how the principle of superposition is used to explain white light at the zero order.

a) (The) displacements (of each wavelength) add to give resultant displacement – B1

b) each wavelength travels the same path difference or are in phase – B1 c) hence a white maximum (is produced) – A0

(ii) Describe how the principle of superposition is used to explain the difference in position of red and blue light in the first-order spectrum (2012/Nov-P21/Q4bi):

a) to obtain a maximum, the path difference must be (equivalent to the multiple of) λ or (the) phase difference (equivalent to the multiple) of 2π rad – B1

b) (Since) λ of red and blue are different – B1 c) maxima (occurs) at different angles / positions – A0

(g) show an understanding of experiments that demonstrate two-source interference using water, light and microwaves

1. The setup to observe interference of waves in ripple tank (2011/Jun-P21/Q7bi,ii):

a) two (ball-type) dippers – M1 b) connected to the same vibrating source /motor (to obtain a coherent source) – A1 c) lamp with viewing screen on opposite side of tank – B1 d) means of freezing picture e.g. strobe – B1

(the observation and analysis portion is the same for both water and light. They are discussed in item (3) below)

2. The setup to illustrate interference using microwaves (transverse waves)

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Explain clearly all the apparatus needed and what each item is used for. For other EM wave, just change the source to other emitters such as light bulb (add an extra slit) and laser.

3. Generalized Observation: on changes that can be observed as a detector is moved along interference fringes formed by light, water or microwaves: a) Explain how the intensity of light alternate between high intensity and low intensity

OR waves superimpose to form regions of constructive interference and destructive interference.

b) Note that the intensity or amplitude of wave is maximum on the zeroth order (i.e., the perpendicular distance between the separation of two slits.

4. Generalized Conclusion:

a) The separation between each consecutive bright fringe/maxima is constant

b) Bright fringe/maxima is formed when the path difference between the two coherent source is a multiple of wavelength (nλ)

5. Changes that can be made to the setup to observe properties of interference patterns (2013-21/6-5d) a) slits made narrower – B1 b) slits put closer together (not just ‘make slits smaller’) – B1

Additional comment: Increase the distance (D) between the source of interference and the wall at which the interference image is formed. This all came from x = Dλ/a and

d sinϴ = nλ

6. Based on the diffraction setup below (2010/Jun-P21/Q4c):

(a) state what effect, if any, the rotation of the grating will have on the interference patterns

- No change for the position for zeroth order diffraction – B1

- 1st and higher order diffraction rotated by 90o – B1

(b) suggest a reason why in certain experiments, the interference patterns are not symmetrical about the centre (e.g., the angle between the two 1st order diffraction is different)

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- Symmetry broken because screen not parallel to grating OR grating not normal to (incident) light – B1

7. Outline how (2009/Nov-P21/Q5c): (i) diffraction may be demonstrated using light.

(a) suitable object, means of observation – M1

(b) laser or lamp and aperture – M1

(c) light region where darkness expected – A1

(ii) interference may be demonstrated using light.

(a) suitable object, means of observation and illumination – B1

(b) light and dark fringes observed – B1

(c) appropriate reference to a dimension for diffraction or for interference – B1

8. Initially, the light passing through each slit (on the setup below) has the same intensity. The intensity of light passing through one slit is now reduced. Suggest and explain the effect, if any, on the dark fringes observed on the screen (2009/Jun-P22/Q5c).

a) amplitudes no longer completely cancel – M1 b) so dark fringes are lighter – A1

Dark fringes can only be obtained when the amplitude of light passing through each slit are the same. Differences in the intensity between the two interfering waves will result in dark fringes getting lighter and bright fringes getting less intense.

(f) show an understanding of the terms interference and coherence

1. Interference: The formation of points of superposition (constructive and destructive) where two coherent waves pass through each other

2. Understand that waves are coherent if there are (2012/Jun-P21/Q6ai): a) constant phase difference – M1 b) between waves – A1

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(h) show an understanding of the conditions required if two-source interference fringes are to be observed

1. Process for microwaves to form constructive interference patterns (2013/Jun-P21/Q5a)

a) waves overlap / meet / superpose – B1 b) coherence / constant phase difference (not constant λ or frequency) – B1 c) path difference = 0, λ, 2λ or phase difference = 0, 2π, 4π – B1 d) same direction of polarization – B1

2. General conditions for constructive interference to occur (2012/Jun-P21/Q6aii): a) path difference is either λ or nλ -- B1 b) phase difference is 360°or n ×360° or n2π rad

3. General conditions for destructive interference to occur (2012-21/6-6aii): a) path difference is either λ/2 or (n+ ½) λ b) phase difference is odd multiple of either 180° or π rad

* State features of a stationary wave that distinguish it from a progressive wave (2010/Jun-P22/Q4a):

a) stationary wave does not transfer energy (no energy transfer) – B1 b) the amplitude of standing wave varies along its length/nodes and antinodes – B1 c) neighboring points (in inter-nodal loop) vibrate in phase, etc. – B1

VERY IMPORTANT!

1. For standing waves, the terms in-phase and phase difference is different to that used for progressive waves.

2. In standing wave, in-phase refers to the fact that all points reaches amplitude simultaneously. Thus every particle along a standing wave is in-phase.

3. Phase difference is no longer the measure of difference in angle between consecutive crest or troughs. It is measure in terms of the difference in position of oscillation. For example, the phase difference in a standing wave between points A and B below.is 180o

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Section V: Electricity and Magnetism

17 Electric fields

(a) show an understanding of the concept of an electric field as an example of a field of force

1. State what is meant by an electric field (2010/Jun-P21/Q5a): a) region/area where a charge experiences a force – B1

define electric field strength as force per unit positive charge acting on a stationary point charge

(b) represent an electric field by means of field lines

a) the lines of force start on a positive charge, and end on a negative charge b) the lines of force are smooth curves which never touch or cross c) the strength of the electric field is indicated by the closeness of the lines, the closer

they are, the stronger the field.

(e) describe the effect of a uniform electric field on the motion of charged particles

1. For a positive charge: (a) positive charge attracted by the negatively charged plates (b) force acting on the charged particle is in the same direction as the electric field

2. For a negative charge: (a) negative charge attracted by the positively charged plates (a) force acting on the charged particle is in the opposite direction of electric field

3. The force experienced by a charge in a uniform electric field is the same regardless of where it is located between the plates.

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19 Current of electricity

(a) show an understanding that electric current is the flow of charged particles

(b) define charge and the coulomb

1. charge = current x time – B1 (2013/Jun-P22/Q6a)

2. coulomb:

a) the SI unit of electrical charge

b) a charge of 1C passes a point when a current of 1A flows for 1s.

(d) define potential difference and the volt

1. p.d. = energy transformed from electrical to other forms

charge – B1 (2011/Nov-P23/Q4a)

2. volt is the potential difference between two points when 1J of energy is transferred by 1C passing from one point to the other

(g) define resistance and the ohm

1. electrical resistance = potential difference / current (2012/Nov-P21/Q2a)

2. Ohm = volt/ampere – B1 (2011/Nov-P21/Q5a)

3. internal resistance: (resistance of the cell) causing loss of voltage or energy loss in cell – B1 (2011/Jun-P22/Q5aii)

(i) sketch and explain the I-V characteristics of a metallic conductor at constant temperature, a semiconductor diode and a filament lamp

1. Metallic conductor

a) The line passes through the origin

(as for an ohmic component)

b) Graph is straight line, where the current is proportional to the voltage applied

c) Obeys Ohm’s law

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2. Filament lamp

a) The line passes through the origin

(as for an ohmic component)

b) For very small currents and voltages, the graph is roughly a straight line.

c) At higher voltages, the line starts to curve.

d) Current no longer proportional to voltage applied.

e) The V/I ratio gets larger.

3. Semiconductor diode

a) Small negative current flow when

negatively biased

b) Small positive current flow when forward bias voltage below threshold voltage

c) Large positive current flow above threshold voltage (2V)

(j)* sketch and explain the temperature characteristic of a thermistor (thermistors will be assumed to be of the negative temperature coefficient type)

a) resistance decreases with increasing temperature

b) typically thousands of ohms at room temperature

c) resistance falls to a few tens of ohms at 100oC

(k) state Ohm’s law

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Ohm’s law states that, for a conductor at constant temperature, the current in the conductor is proportional to the potential difference across it.-

(m) define e.m.f. in terms of the energy transferred by a source in driving unit charge round a complete circuit

(n) distinguish between e.m.f. and p.d. in terms of energy considerations

From (2012/Nov-P23/Q4a):

a) e.m.f. = chemical energy to electrical energy – M1 b) p.d. = electrical energy to thermal energy – M1 c) idea of per unit charge – A1

(o) show an understanding of the effects of the internal resistance of a source of e.m.f. on the terminal potential difference and output power.

1. A battery delivers the maximum power to a circuit when the load resistance of the circuit is equal to the internal resistance of the battery.

2. When load resistance is zero, power dissipated by load is zero because P=I2R

3. When load resistance is very large, power dissipated gets very small as the current through the load is reduced significantly.

20 D.C. circuits

(c) recall Kirchhoff’s first law and appreciate the link to conservation of charge

From (2012/Jun-P23/Q5ai,ii)

a) Kirchhoff’s first law: sum of currents into a junction = sum of currents out of junction – B1

b) KFL is linked to the conservation of charge – B1

(d) recall Kirchhoff’s second law and appreciate the link to conservation of energy

From (2012/Jun-P21/Q5ai,ii)

a) Kirchhoff’s second law: sum of e.m.f.’s = sum of p.d.’s around a loop/circuit – B1

b) KSL is linked to the conservation of energy – B1

(j) show an understanding of the use of a potential divider circuit as a source of variable p.d.

1. In using a potential divider to measure the R, I and V of a wire (2012/Nov-P21/Q2bi)

a) metal wire in series with power supply and ammeter – B1 b) voltmeter in parallel with metal wire – B1 c) rheostat in series with power supply or potential divider arrangement or a variable

power supply – B1

(k) explain the use of thermistors and light-dependent resistors in potential dividers to provide a potential difference that is dependent on temperature and illumination respectively

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a) At low temperatures, resistance of thermistor is high

b) Most electrical energy dissipated by thermistor hence the potential drop across the thermistor is large.

c) Vout increases

d) At high temperatures, the resistance of thermistor drops.

e) The potential drop across thermistor reduces

f) Vout reduces accordingly.

a) At low illumination, resistance of

LDR is high

b) Most electrical energy dissipated by

LDR hence the potential drop

across the LDR is large.

c) Vout increases

d) Under strong illumination, the

resistance of LDR drops.

e) The potential drop across LDR

reduces

f) Vout reduces accordingly.

Section VI: Modern physics

27 Nuclear physics

(a) Infer from the results of the α-particle scattering experiment the existence and small size of the nucleus.

The deflection of α-particles by a thin metal foil is investigated with the arrangement shown in figure below. All the apparatus is enclosed in a vacuum. The detector of α-particles, D, is moved around the path labelled WXY

1. Describe the two main results of the α-particle scattering experiment (2013/Jun-P21/Q7a):

a) the majority (of alpha particles) /most went straight through or were deviated by small angles – B1

b) a very small proportion/a few were deviated by large angles – B1

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c) small angles described as < 10° and large angles described as >90° – B1

2. Relate each of the results above with the conclusions that were made about the nature of atoms (2013/Jun-P21/Q7b):

a) most of the atom is empty space/nucleus very small compared with atom – B1 b) mass and charge concentrated in (very small) nucleus – B1

c) the nucleus of an atom is positively charged, which causes the α-particles to deflect due to repulsive force.

d) as atoms are neutral, the atom must contain negative particles.

Please take note that the experimental results provided the evidence for the physical properties of atoms. For example, on the conclusion that atoms are mostly empty space is deduced from the fact that the majority of α-particle went straight through the atom. Also, it can be concluded that the mass of an atom is concentrated in a very small nucleus due to the large deviations experienced by the α-particle (2010/Nov-P22/Q7a)

3. Explain why the apparatus is enclosed in a vacuum (2012/Nov-P21/Q6bi):

a) Vacuum is needed because α-particle travels short distance in air (energy loss from collisions with air molecules) – B1

4. Gold foil is used in the experiment because it can be made very thin (only up to a few hundred atoms thick).

5. The a-particles in this experiment originated from the decay of a radioactive nuclide. Suggest two reasons why β-particles from a radioactive source would be inappropriate for this type of scattering experiment (2010/Nov-P22/Q7b):

a) β-particles deviated by (orbital) electrons – B1 b) β-particle has (very) small mass – B1 c) β-particles have a range of energies – B1

* Do not allow β-particles have negative charge or β-particles have high speed

(b) Describe a simple model for the nuclear atom to include protons, neutrons and orbital electrons (aka the nuclear model of an atom).

1. Describe in detail an atom of uranium-235 (2013/Jun-P23/Q7ai):

a) nucleus contains 92 protons – B1 b) nucleus contains 143 neutrons (missing ‘nucleus’ 1/2) – B1 c) outside / around nucleus (contains) 92 electrons – B1 d) most of atom is empty space / mass concentrated in nucleus – B1 e) total charge is zero – B1 f) diameter of atom ~ 10–10 m or size of nucleus ~ 10–15 m – B1

2. Scientist originally viewed atoms as a neutral particle made up of lumps of negative and positive charges mixed together. This is known as the plum pudding model.

3. Rutherford later proposed and verified the correct structure of an atom, which consist of

a) mostly empty space b) has a dense nucleus with orbiting electrons around it c) this is known as the nuclear model of the atom.

(c) distinguish between nucleon number and proton number

1. Nucleon number – the number of protons together with the number of neutrons in the nucleus is called the nucleon number (or mass number) A

2. Proton number – the number of protons in the nucleus of an atom ( aka atomic number) Z

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(d) show an understanding that an element can exist in various isotopic forms, each with a different number of neutrons

1. With reference to the two forms of uranium (uranium-235 and uranium-238) explain the term isotopes (2013/Jun-P23/Q7aii):

a) Nucleus must have the same number of protons – B1 b) Nuclei have different number of neutrons (list down the respective nucleon

number) – B1

(f) appreciate that nucleon number, proton number, and mass-energy are all conserved in nuclear processes

1. Explain why mass seems not to be conserved in the reaction below (2013/Jun-P22/Q7aii):

a) mass-energy is (always) conserved – B1 (as opposed to mass conservation alone) b) mass is less because energy is released – B1

* item (b) should be explained in terms of E=mc2 – B1 (2013/Jun-P23/Q7bii)

c) Energy emitted in the form of kinetic energy of the products / γ-radiation photons / e.m. radiation – B1 (2012/Jun-P21/Q7b)

2. In a nuclear reaction, proton number and neutron number are conserved. Other than proton number and neutron number, state a quantity that is conserved in a nuclear reaction. (2011/Nov-P21/Q7bi): a) Momentum

(h) show an appreciation of the spontaneous and random nature of nuclear decay

1. State the experimental observations that show radioactive decay is spontaneous (2011/Nov-P22/Q7ai):

a) the half life / count rate / rate of decay / activity is the same no matter what external factors / environmental factors – B1

* other environmental factors include chemical / pressure / temperature / humidity

(2012/Nov-P23/Q6aiii)

2. State the experimental observations that show radioactive decay is random:

a) the observations of the count rate / count rate / rate of decay / activity / radioactivity during decay shows variations / fluctuations – B1 (2011/Nov-P22/Q7aii)

b) time of decay (of a nucleus) cannot be predicted OR nucleus has constant probability in a given time – B1 (2009/Nov-P22/Q7bii)

3. Explain what is meant by radioactive decay (2010-23/11-9a). a) Nucleus emits α-particles or β-particles and/or γ-radiation – B1 b) to form a different / more stable nucleus – B1

4. Suggest why some radioactive sources are found to contain traces of helium gas (2010/Nov-P23/Q9biii):

a) if the source is an α-emitter – B1 b) α-particles stopped within source (and gain electrons) – B1

5. When unstable nucleus undergoes radioactive decay, the atom will be affected as follows: a) α-decay, the nucleon number decreases by 4 and the proton number decreases by

2.

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b) β-decay, the nucleon number is unchanged and the proton number increases by 1. c) In γ-emission there is no change in nucleon or proton number.

(i) show an understanding of the nature and properties of α-, β- and γ- radiations

1. State what is meant by an α-particle (2010/Jun-P23/Q7ai): (d) either helium nucleus OR particle containing two protons and two neutrons – B1

2. β-particles are fast moving electrons.

3. γ- radiation is part of the electromagnetic spectrum with wavelengths between 10-11 m and 10-13 m.

4. Radioactivity can be detected using a Geiger counter, photographic plates, and a scintillation counter

5. State the properties of α radiation (2012/Jun-P21/Q7aii):

a) Can be deflected in electric/magnetic fields – B1 b) absorbed by thin paper or few cm of air (3cm → 8cm) (not low penetration) – B1 c) mass 4u (1u ≈ 1.66 x 10-27 kg) – B1 d) highly ionizing – B1 OR causes dense ionisation in air (2010/Jun-P22/Q7aii) e) contains 2 protons + 2 neutrons – B1 (2008/Jun-Q7a)

6. Explain the process by which α-particles lose energy when they pass through air (2011/Nov-P22/Q7c):

a) collision with molecules – B1 b) causes ionisation (of the molecule) / electron is removed – B1

7. State two properties of β-radiation (2012/Nov-P23/Q6aii):

a) can be deflected by electric and magnetic fields or negatively charged – B1 b) absorbed by few (1 – 4) mm of aluminum – B1 c) 0.5 to 2m for range in air – B1 d) speed up to 0.99c – B1 e) it is an electron – B1 (2008/Jun-Q7a)

8. Distinguish between an α-particle and a β-particle (2008/Jun-Q7a): a) α –particle is a helium nucleus or contains 2 protons + 2 neutrons BUT β-particle is

an electron – B1 b) α-particle’s speed < β-particle’s speed – B1 c) α-particle has discrete values of speed/energy BUT β-particle has continuous

spectrum of energy – B1 d) α-particle’s ionising power >> β-particle’s ionising power – B1 e) α-particle’s range << β-particle’s range – B1 f) α-particle has positive charge, β-particle has negative charge – B1 g) α-particle’s mass > β-particle’s mass

9. Summary of properties of α-, β- and γ- radiations from (2011/Nov-P22/Q7b):

Property α-particle β-particle γ-radiation

charge 2e -e 0

mass 4u 9.11 x 10-31 kg 0

speed 0.01 – 0.1 c Up to 0.99 c c

nature helium nucleus electron short-wavelength EM wave

penetrating power few cm of air few mm of aluminium

few cm of lead

relative ionizing power

104 102 1

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affected by photographic film

yes yez Yes

deflected by electric/magnetic

fields

yes yes no

IMPORTANT: You must memorize the table above

10. A radioactive source emits α-radiation and γ-radiation. Explain how it may be shown that the source does not emit β-radiation using the absorption properties of the radiation (2012/Jun-P23/Q7a): a) thin paper reduces count rate hence α – B1 b) addition of 1cm of aluminium causes little more count rate reduction hence only

other radiation is γ – B1

11. A radioactive source emits α-radiation and γ-radiation. Explain how it may be shown that the source does not emit β-radiation using the effects of a magnetic field on the radiation (2012/Jun-P23/Q7a):

a) magnetic field perpendicular to direction of radiation – B1 b) look for a count rate in expected direction / area if there were negatively charged

radiation present. If no count rate recorded then β not present. – B1

12. Two horizontal metal plates are separated by distance din a vacuum. A potential difference V is applied across the plates, as shown in figure below.

A horizontal beam of α-particles from a radioactive source is made to pass between the plates. State and explain the effect on the deflection of the α-particles for each of the following changes: (2011/Nov-P23/Q6a):

a) The magnitude of V is increased. (e) greater deflection – M1

b) The separation d of the plates is decreased

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(f) hence more force on the particle – A1

13. α-radiation is the most strongly ionizing because: a) of its large mass (≈1840 heavier than β-particles) b) has a charge of 2e c) is slower moving compared to β-particles (higher probability of interaction to take

place)

14. β-radiation is less ionizing because its: a) relatively small mass (approx. 1840 times lighter than α-radiation) b) has single charge –e c) is faster compared to α-radiation

(j) infer the random nature of radioactive decay from the fluctuations in count rate

1. State how the random nature of radioactive decay may be inferred from observations of the count rate (2010/Nov-P23/Q9bi). a) fluctuations in count rate (not ‘count rate is not constant’) – B1

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9702 Physics - Definitions and Statements v1.0