97743707 physics-exam-study-notes

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Physics Exam Study Notes

1: Forces and Motion Kinematics: study of motion Basic types of motion:

o Uniform (constant speed in straight line)o Non-uniform

Scalar quantity:with magnitude & no directiono Distance, average speed

Vector quantity: with magnitude (arrow above it) & direction (in square brackets after unit)o Position, displacement, acceleration

Velocity:o Rate of change of positiono Average velocity: displacement divided by time interval for that changeo 2-D motion: using GPS (global position system)

N/S/E/W to communicate directions Ex: 5.0 cm [25° S of E] or [E25°S]

Acceleration: rate of change of velocity V-t graph to find other things:



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o Area under line gives displacement, slope gives acceleration Resultant displacement of 2 dimensions:

o Vector sum of individual displacementso Use Pythagorean Theorem and SOH-CAH-TOA

Relative motion: velocity of a body relative to a particular frame of reference Methods of writing direction:

o GPS = [E25°S] or [25° S of E]o Bearing = [N 160°] (measure CW from North position)

2: Energy Dynamics: causes of motion Force: push or pull, vector quantity

o 4 fundamental forces: gravitational, electromagnetic, strong nuclear, weak nuclear Unit of force: Newton (N) -> 1N = 1(kg x m)/s2

Net force/resultant force: vector sum of all forces acting on an object Mass: quantity of matter in an object (standard: kg)

Weight: force of gravity on an object (Fg), measured in Newton’s

Newton’s Laws of Motion:1. If the net force acting on an object is zero, the object will maintain its state of rest or constant

velocity.2. If the external net force on an object is not zero, the object will accelerate in the direction of

that net force. The magnitude of the acceleration is proportional to the magnitude of the net force and inversely proportional to the object’s mass.

3. For every action force, there is a reaction force equal in magnitude but opposite in direction. Law of Universal Gravitation:Force of gravitational attraction between any two objects is directly

proportional to the product of the masses of the two objects, and inversely proportional to the square of the distances between their centres.

Friction:

Static friction (Fs): force that tends to prevent a stationary object from starting to moveo Starting Friction: max static friction, amount of force to overcome to get object to move

Kinetic friction (FK): force that acts against an object’s motion in a direction opposite of the direction of motion

o Sliding friction, rolling friction, fluid friction Coefficient of friction (µ): number that indicates the ratio of the magnitude of the force of

friction (Ff) between 2 surfaces to the magnitude of the force perpendicular to these surfaces

o µK for FK, µs for Fs; larger means more friction

Energy: Energy: capacity to do work

o 1 J (joule) = 1 Nm = 1(kg x m2)/s2

o Forms: thermal, electrical, radiant, nuclear potential, gravitational potential, kinetic, elastic potential, sound, chemical potential

Work: energy transferred to an object by an applied force over a measured distanceo Power: rate of doing work or transforming energy

1 W = 1 J/s Gravitational potential energy: energy possessed by an object because of its position relative to

a lower position Kinetic energy: energy possessed by an object due to its motion Law of Conservation of Energy: energy cannot be created nor destroyed. When energy changes

from one from to another, no energy is lost.o Valley problems, pendulum problems, objects dropped from a height

(mvA2)/2 + mghA= (mvB

2)/2 + mghB

o Ramp problems

Moving up: (F – Ff) ∆d =mgh

Moving down: mgh – Ff∆d = ½mv2

Thermal Energy: Thermal energy: total kinetic energy and potential energy (caused by electric forces) of the

atoms or molecules of a substance Temperature: measure of the average kinetic energy of the atoms or molecules of a substance Heat: transfer of energy from a warmer body to a cooler one 3 methods of heat transfer:

o 1: Conduction: heat transferred through a material by collisions of atomso 2: Convection: heat transferred by a circulating path of fluid particles called “convection

current”o 3: Radiation: process of heat transfer by electromagnetic waves (requires no particles)

3 factors that determine how much energy it takes to heat up an object:o Object’s mass, temperature change, and substance’s specific heat capacity

Specific heat capacity: J/kg°C Principle of heat exchange: when heat is transferred from one body to another, the amount of

heat lost by the hot body equals the amount of heat gained by the cold body If enough change in thermal energy occurs, a substance will change states

Latent heat: Extra stored heat when phase changes Latent: “hidden” During melting or vaporization, heat added won’t cause a rise in temperature

Temp. of a substance will change until a critical temp. is reached, at which the substance will change phase to facilitate the temp. change

Latent heat of fusion (Lf): latent heat released during freezingo Amount of heat energy needed to melt 1.0kg of material

Latent heat of vaporization (Lv): latent heat stored when heat is added during vaporizationo Amount of heat energy needed to vaporize 1.0kg of material

Nuclear energy: Fission: split, fusion: join

o Fission releases enormous amounts of energy in the form of heat or radiationo Fusion used in the sun, creates less radioactive material

Nuclear isotopes: atoms of the same element with same # of protons, but diff. # of neutronso Deuterium: hydrogen 2, tritium: hydrogen 3

Alpha particles: speed of about 107 m/so Positively charged (+2) Helium nucleus, mass of 4 atomic mass unitso Low charge, ionizes with other atoms stronglyo Low penetrating power

Beta particles: speed of about 108 m/so Charge of -1, mass of about 1/2000th of a proton (same as electron)o Ionizes atoms that they pass, but not as strongly as alpha particleso Medium penetrating power, stopped by aluminum foil

Gamma rays: waveso No mass or chargeo Do not directly ionize other atomso High penetrating power, would take a thick metal to stop them

Law of Conservation of Mass-Energy: for an isolated system, the total amount of mass-energy remains constant

Atomic mass (A) = # of protons (Z) + # of neutrons (N)o Naming convention: mass above # of protons; left of chemical symbolo Proton (1

1p), neutron (10n), electron (0

-1e)

3: Waves and SoundVibrations:

Vibration: periodic motion when it repeats a pattern of motion 3 types of vibrations:

o Transverse: perpendicular to its axis at normal rest position (ex. pendulum)o Longitudinal: parallel to its axis of rest position (ex. pogo stick)o Torsional: around its axis at rest position (ex. motion of steering wheel)

Cycle: 1 complete oscillation or 1 complete vibration/1 complete wave Frequency (f): # of cycles per second, measured in Hertz (Hz)

Period (T): time for 1 cycle, measured in seconds Amplitude: distance in either direction from the rest position to an extreme position (max

displacement) In Phase: objects have same period & pass through the rest position at the same time Out of Phase: objects don’t have the same period & pass through the rest position at the same

time

Waves: Wave: vibration/disturbance that can transfer energy over a distance Transverse waves: particles in the medium vibrate at right angles to the direction in which the

waves travel (ex. water waves/waves in a rope)o Crest/trough, node/antinode, amplitude, rest axis

Longitudinal waves: particles vibrate parallel to the direction of wave motion (ex. sound waves/compress coils in a Slinky)

o Compression/rarefaction Wave interference: occurs when 2 act simultaneously on the same particles of a medium

o Constructive interference: creates supercrests and supertroughs (add 2 together)o Destructive interference:waves diminish one another, amplitude decreases

Standing waves: special case of inference in a one-dimension mediumo If colliding waves are controlled so they have the same amplitude and wavelength but in

opposite directions, it results in a “standing wave interference pattern” Principle of Superposition: at any point, the resulting amplitude of 2 interfering waves is the

algebraic sum of the displacements of the individual waves Resonance: response of an object that is free to vibrate to a periodic force with the same

frequency as the natural frequency of the objecto Mechanical resonance: if physical contact between the periodic force & the objecto Ex: Tacoma Narrows bridge, rock a car stick in snow, child moving on swing

Sound: All sounds stimulate the auditory nerve Humans respond to sound frequencies between 20Hz – 20,000Hz

o Infrasonic: lower than 20Hz, ultrasonic: above 20,000Hz Produced by vibrating objects (ex. guitar string, throat vibrating, stereo speaker) Needs a material medium for transmission Sound waves are longitudinal waves Larger amplitude: louder sound, higher frequency: higher pitch Intensity of sound:

o Sounds audible to humans can vary in intensity Loudness measured in bels (B), most people use decibel scale (dB)

o 1dB = 1/10B or 10dB = 1B 0dB: threshold of hearing (10-12W/m2)

85dB: must wear eat protection for industrial safety 130dB: threshold of pain (101W/m2) 160dB: instant perforation of ear drum (104W/m2)

o Each rise of 10dB: 10 fold increase in sound intensity Interference between identical sound waves: causes louder/softer sound regions

o Can be done with 2 loudspeakers in phase Noise cancellation headphones use destructive interference (exactly out of phase with outside

noise), can remove 70% of external noise Beat: periodic change in sound intensity Beat frequency: # of beats heard per second, in hertz Doppler Effect: observed frequency increases when source of sound approaches, and vice versa

Sound Barrier: When flying at speed of sound, the wave fronts in the front of a plane pile up, producing an reap

of very dense air/intense compressiono Extra thrust required to break through barriero Aircraft must be designed to “cut through” or it will be buffeted disastrously

Speed of sound: 332m/s or 1200km/h or 750mi/h at 0°Co Subsonic speeds: slower than speed of soundo Supersonic speeds: faster than speed of sound

Sonic boom: invisible cone behind aircraft, sound waves interfere constructivelyo Intense acoustic pressure waves sweeps along the groundo Occurs as 2 large cracks (like thunder or a muffled explosion)

Echolocation: Echoes: produced when sound is reflected by a hard surface Echolocation: location of an object using reflected sound SONAR: Sound Navigation and Ranging

Music: Music: combination of musical notes

o Musical notes originate from a source vibrating in a uniform manner with one or more constant frequencies

o 3 main characteristics of musical sounds: pitch, loudness, quality Noise: originates from a source vibrating where frequencies are constantly changing in a random

manner Pitch: related to frequency

o Bass notes lower in pitch than treble noteso Bass notes have a longer wavelength than treble notes

Note: a pure tone is a sound where only one frequency is heard Musical sounds usually combinations of sounds

Chord: series of sounds where their frequencies are in simple ratios (4:5:6:8)o Sounds very pleasing or harmoniouso Chords have a high level of consonance

Unpleasant sounds have high dissonance or low consonance Octave: successive doubling of frequencies Scientific Musical Scale: middle C is 256Hz

o C# and D aren’t the same frequency on the diatomic scale Musical/Equitempered Scale: A4 is 440Hz

o C4 is 261.6Hzo Exactly 12 intervals per octaveo Each note found by multiplying the previous by 1.059 (found by taking the 12 th root of 2)o C# and D are the same frequency

4 factors that affect the frequency of a vibrating string:o Length (L), tension (F), diameter (d), density (D)

Quality of sound: In a vibrating stretched string and the fundamental mode of vibrating, the string vibrates in one

segment with a node on each end and one antinode in the middle. This creates f0 or fundamental frequency.

Different frequencies can be produced by forcing the string to vibrate in different patternso Frequency produced depends on number of nodes/antinodes

Second harmonic (2f0) same as first overtone, 3 f0 = second overtone, etc.o Frequencies of overtones are in simple whole numbered multiples of the fundamental

and are called harmonicso Overtones can be more intense than fundamental in some instruments (ex. clarinet)

Quality of a musical note depends on the # and relative intensity of the overtones it produces along with the fundamental

Tuning fork only has one fundamental frequency

Resonance in air columns: Closed air columns:

o Caused by standing wave pattern with node at closed end & antinode at open endo For fixed length: resonance first occurs when air column is ¼ λ (wavelength)

Then: 3/4 λ, 5/4 λ, 7/4 λ etc. Open air columns:

o Created by standing wave patterns set up in a tube where an antinode exists at BOTH open ends

o For fixed length open columns: resonance first occurs at λ/2 (first harmonic)

o Then:λ, 3λ/2, 2 λ, etc.

4: Electricity and MagnetismElectrostatics:

Static electricity: a build-up of stationary electric chargeo Charging by friction: rubbing 2 objects together

Fundamental laws of electric charge:o Opposite charges attract, similar charges repel, charged objects attract some neutral

objects Change in charge due to loss/gain of electrons only Conductors: solids in which charge flows freely (most metals, water) Insulators: solids that hinder the flow of charge (glass, rubber, wood, plastic, concrete)

Electric fields and electric charge: Every charged object creates an electric field of force in the space around it

o Relative distance between adjacent field lines at a given point is an indication of the strength of the electric field at that point

Magnitude of the electric force of the attraction or repulsion is:o Directly proportional to the product of the chargeso Inversely proportional to the square of the distances between them

One coulomb (C) of energy made up of 6.24x1018e-

Electric current: Rate of movement of electrically charged particles past a point When electric charges move from 1 place to another In metals: moving charges are electrons Measured in amperes (A)

o 1A = 1C/so Standard household fuse: 15A

Conventional current: positive charge from + to – (used in this course) o Electric flow: negative charge from – to +

Can flow in either direction in liquids & gases Batteries: DC, wall sockets: AC Ammeter: measures amount of electric current in a circuit

Electrical potential difference: Amount of work required per unit of charge (coulomb) to move a positive charge from one point

to another in the presence of an electric field A 1V battery performs 1J of work to move 1C of charge between its terminals

o 1V = 1J/C

Electrical resistance: Opposition experienced when charges pass through a material or device, resulting in a loss of

electrical potential energy Ohm’s law: The potential difference between any 2 points in a conductor varies directly as the

current between the 2 points as long as the temp.remains constant. Unit for resistance: ohm (Ω)

o 1Ω = 1V/1A

Electric circuits: Series:

o VT = V1 + V2 + V3

o IT = I1 =I2 =I3

o RT = R1 + R2 + R3

Parallel:o VT = V1= V2= V3

o IT = I1+ I2+ I3

o RT-1 = R1

-1 + R2-1 + R3

-1

Kirchhoff’s Laws: Kirchhoff’s Voltage Law: as you move through a circuit, all of the voltage increases must equal all

of the voltage decreases Kirchhoff’s Current Law: at any junction point in an electric circuit, the total current into the

junction is equal to the total current out of the junction

Power in electric circuits: Measured in watts (W)

o J/s = J/C x C/s

Cost of electricity: Use kilowatt for power and hours for time

o Unit used is kilowatt-hour (kWh) instead of joules, since it’s larger Better to send electrical energy at high voltages & low current to minimize power loss

Electromagnetism: Poles: areas of concentrated magnetic force North pole: end of a magnet that seeks northerly direction Sound pole: end of a magnet that seeks southerly direction Law of Magnetic Poles: opposite poles attract, like poles repel Magnetic field of force: space around a magnet in which magnetic forces are exerted Characteristics of magnetic field lines:

o Spacing of lines indicates relative strength of force (closer = stronger force)

o Have direction (N → S outside, S → N inside a magnet)o Do not touch each othero Outside: magnet lines are concentrated at poles, inside: magnet lines are the closest

together Compass needle always points in the direction the field lines are going outside the magnet Ferromagnetic substances can become magnetized

o Iron, nickel, cobalt (or any alloy containing them) Whenever a current moves through a conductor, a magnetic field is created in the region

around the conductor

Domain Theory of Magnetism: Atoms of ferromagnetic substances are like tiny magnets

o Called “dipoles”, interact with neighbouring dipoleso Groups line up with their magnetic axes in the same direction to form a magnetic

domain Domains: clusters of 1017 atoms

Non-magnetized: randomly pointing domains

Effects:o Magnetic induction

Permanent magnet near iron nail: temporary magnet Field of perm. cause dipoles in nail to align momentarily Soft iron: if nail loses magnetism as moved away Hard iron: if nail retains magnetism as moved away

o Demagnetization Aligned dipoles return to random directions Caused by dropping or heating Some materials revert when removed from magnetic field (i.e. pure iron) Materials that instantly demagnetize: soft ferromagnetic materials Alloys used to make hard ferromagnetic materials (use aluminum or silicon)

o Reverse magnetization Poles reversed when magnet placed in a strong enough magnetic field with

reverse polarityo Breaking a bar magnet

Creates mini magnet with identical dipole alignmento Magnetic saturation

Peak of magnet’s strength: when max # of dipoles alignedo Induced magnetism by Earth

Dipoles will align if a piece of iron with agitated atoms by heating or mechanical vibration in Earth’s magnetic field

Point north & at angle of inclination + tapping with a hammer

Steel columns, hulls, and railroad tracks tend to magnetizeo Keepers for bar magnets

Bar magnets demagnetize over time as poles start to reverse the dipoles’ polarity (random thermal motion of atoms)

Store in pairs with opposite poles adjacent & small pieces of soft iron (keepers) across ends to prevent demagnetization

Keepers become strong induced magnets, form closed loops

Factors affecting the magnetic field of a coil: Coil’s magnetic field can be turned on/off & alter strength Strength related to degree of concentration of its magnetic field lines More current in the coil = greater concentration of magnetic field lines in the core

o 2x current = 2x magnetic field strength Number of loops in the coil:

o Each loop of wire produces its own magnetic fieldo Magnetic field of a coil: sum of the magnetic fields of all its loopso 2x loops in coil = 2x magnetic field strength

Type of core material:o Material of core affects coil’s magnetic field strength

Cylinder of iron (instead of air) = 1000+ times stronger Aluminum core = no effect

o Core material becomes induced magnet, magnetic field strength increases Dipoles align with magnetic field of the coil

o Relative magnetic permeability (K): factor by which a core material increases the magnetic field strength that would exist in the same region if a vacuum replaced it

o 2x relative magnetic permeability of the core = 2x strength Ferromagnetism, paramagnetism, and diamagnetism

o Core materials divided into 3 groups according to their relative magnetic permeabilityo Ferromagnetic: high, strong induced magnetso Paramagnetic: slight increase, slightly greater than 1

Oxygen and aluminumo Diamagnetic: slight decrease, slightly less than 1

Copper, silver and water

Motor Principle: A current carrying conductor that cuts across external magnetic field lines, experiences a force

perpendicular to both the field lines and the direction of the electric current Applications: moving coil loudspeaker, galvanometer (armature forced to pivot with increased

current)o Voltmeter: galvanometer + high value resistor in serieso Ammeter: galvanometer + low value “shunt” resistor in parallel

Electric motor: device that can convert electrical potential energy into mechanical energyo DC motor: needs DC electricity, uses “split right commutator” to reverse current

through armatureo AC motor: needs AC electricity, uses “slip rings” attached to armature since current

switches direction, no need for split ring

Generator Principle: A current can be induced by moving a conductor through a magnetic field

Right Hand Rules: Conductor (straight):

o Thumb points in direction of current flowo Curled fingers point in direction of magnetic field lines

Coil/solenoid:o Thumb points in direction of the field lines inside the coil (towards N)o Coil grasped with fingers pointing in direction of current flow

Motor:o Thumb points in direction of current through straight conductoro Fingers point in direction of external magnetic field lineso Palm shows direction of force on the conductor

Generator:o Thumb points in direction of forceo Fingers in direction of field lineso Palm shows direction of current

Electromagnetic Induction: An electric current produces a magnetic field, therefore reverse is true Faraday’s Law of Electromagnetic Induction: an electric current is induced in a conductor

whenever the magnetic field in the region of the conductor changes Factors that affect magnitude of induced current:

o Number of turns on coil, rate of change of inducing magnetic field, strength of inducing magnetic field

Induced magnetic field of coil opposes the action of the external magneto If bar magnet going in, coil’s N is at the top; and vice versa

Lenz’s Law: for a current induced in a coil by a changing magnetic field, the electric current is in such a direction that its own magnetic field opposes the change that produced it

Transformers:(robots in disguise)

An electrical device that can increase or decrease voltages Can only be AC, induction coils DC voltages (in automobiles) Step up transformer:

o Used to increase AC voltageso As current supplied to primary coil reverses, it continually changes magnetic field of iron

coreo Induces a current to flow on the secondary coilo Have more coils on secondary coil than on primary coil

Step down transformer:o Used to decrease AC voltageso Ex: train set, car race car transformers, power adapters

Adapter : step down transformer + rectifier (AC to DC convertor) in series

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97743707 physics-exam-study-notes