Paper 3

Question 1

Absolute motion

Answer 1

A principle disproved by Michelson and Morley experiment, the idea that it is constant across the universe, Newton and Galileo assumed space and time to be absolute quantities

Question 2

A gas discharge tube

Answer 2

Gas at a low pressure subject to a high potential difference, the electric field ionises atoms leading to the production of cathode rays due to the absorption of positive ions into the cathode causing free electrons to be iodised

Question 3

Negative glow

Answer 3

Slower moving electrons at the cathode being captured by positive ions leading to the emissions of photons

Question 4

Positive column

Answer 4

The accelerating electrons which are attracted towards the anode cause excitation by collision, when electrons of gas atoms then return to ground state a characteristics coloured glow is produced

Question 5

Thermionic emission

Answer 5

Free electrons ionised due to the heating of the filament by a current flowing through it, provides energy

Question 6

How did they determine cathode rays were charged

Answer 6

Found to be deflected by magnetic fields, so the paddle wheel motion stopped

Question 7

Why did the paddle wheel move

Answer 7

Paddle wheel gains energy from cathode rays, transfer of momentum, always move from cathode to anode so movement due to cathode rays

Question 8

Determining the specific charge of the electron

Answer 8

Used an electron gun (thermionic emission) and then a uniform magnetic OR electric field, a velocity selector meant “v” was known and the same for all, Deflection by an electric field or magnetic field was then used

Question 9

Equation for specific charge from experiments

Answer 9

Electric fields using F=ma, d= distance between plates, s=deflection
(F/m)=(2s/t²)
(e/m)=(2sd/t²V)

Magnetic field,
Bev=(mv²/r)
(e/m)=(v/Br)

Question 10

Thompson’s conclusion

Answer 10

Electron’s are negatively charged particles with energy mass and momentum, the high specific charge shows it has much less mass than a alpha particle
The specific charge was independent of the metal it emitted from so it’s fundamental to matter

Question 11

Milikan oil drop experiment

Answer 11

1.find the terminal velocity of the droplet and use Stokes law,this is used to find mass
2. Adjust the p.d until the oil drop is stationary so that the electrostatic force equals the weight
3. Repeat

Question 12

Equations for oil drop experiment

Answer 12

mg=6πηrv
m=(4/3)πr³ρ
r²=(9/2)(vη/ρg)
(V/d)e=mg
r is used to find m and m is used to find e

Question 13

Conclusion from Milikan experiment

Answer 13

The charges of oil drops where found to all be multiples of 1.6x10^-19, this means charge of electrons was quantised

Question 14

Newton’s corpuscular theory

Answer 14

A stream of tiny particles, reflect by bouncing of the mirror with no loss of velocity, refraction explained by the parallel component being unchanged amd the perpendicular velocity increasing as it’s attracted to the medium

Question 15

Huygens theory of light

Answer 15

Longitudinal wave moving through the ether, points on wavefronts produce secondary wavelets that spread out. Reflection due to secondary wave fronts and refraction, the wave moves slower in the transparent substance

Question 16

The ether

Answer 16

A proposed medium for light which was assumed due to the knowledge that sound required a medium. Disapproved by the Michelson-Morley experiment

Question 17

Youngs double slit

Answer 17

Monochromatic light from a coherent source passing through a double slit produced an interference pattern of light and dark fringes, Newtons theory instead predicted two bright bands. So light is shown to be a wave

Question 18

Fizeau speed of light

Answer 18

The rotating wheel cuts the beam of light into pulses which are reflected by a mirror
When cog rotation speed is slow light returns through original gap.
When f⁰ is reached no light can be seen as the light is blocked by a tooth, exactly replaced by a tooth in the time taken for reflection.
Any odd multiple of f⁰ will then also block the light (3f,5f …)

Question 19

Fizeau calculation

Answer 19

2D/c=1/2f⁰N
N is teeth on cog
c=4Df⁰N

Question 20

Maxwells theory

Answer 20

Mathematically linked electric and magnetic fields discovering electromagnetic waves, showing them to be transverse in nature with the two inphase

Question 21

Speed of an EM wave

Answer 21

c=1/(με)½
This was shown to match recorded values of the speed of light, therefore light must be an EM wave

Question 22

Ηertzs experiment to find EM waves

Answer 22

Detecting radio waves with a spark due to a voltage jump across an air gap, this is due to an induced emf from the detector in an oscillating electric field

Question 23

Recording a radio waves wavelength

Answer 23

A standing wave was produced by reflecting the radio wave on a metal sheet, the nodes (points where no signal could be detected) where used to find the λ

Question 24

The ultraviolet catastrophe

Answer 24

Wave theory predicted the wavelength of blackbody radiation to increase with temperature exponentially, this doesn’t fit with experimental data
Plank solved this problem quantifying the energy with the constant h so that E=hf

Question 25

Photoelectric effect

Answer 25

Showed the particle nature of light as intensity didn't effect electron emission, frequency did Einstein explained this with the photon theory of light, wave packets with energy hf Also there was no delay which was predicted by the wave theory

Question 26

Wave particle duality

Answer 26

Light has both a particular and wavelike nature, this was used for de Broglie to propose all particles mave have a wavelike nature The de Broglie wavelength λ=h/mv

Question 27

Transmission electron microscope

Answer 27

A TEM has 3 lenses Condenser lense use a magnetic field to make a wide parallel beam of electons incident uniformly on a thin sample Objective lenses forms the first image which is magnified amd inverted, by scattered electrons Magnifying lenses can magnify or correct orientation The image is projected in to a fluorescent screen

Question 28

What factors affect the quality of a TEM image

Answer 28

Resolution is dependent on the de Broglie wavelength, a shorter wavelength means greater resolving power, so increasing the speed/energy of the electrons would increase detail of the image Variation in electron speed would decrease the detail of the image, uneven sample width will reduce electrons speed unevenly giving a blurred image

Question 29

The scanning tunnelling microscope

Answer 29

The electrons are considered as a wave of probability, tunnelling current is increased when gap is reduced so can be used to produce an image of the surface The de Broglie wavelength of the electron must be sufficiently long to stretch across the gap giving the electrons a finite probability of crossing the gap

Question 30

Limits of scanning tunnelling microscope

Answer 30

Gap must be less than 1nm so amplitude is similar enoug, too large and the current is negligible Too small a gap could lead to the damage of the tip by collision

Question 31

The Michelson Morley experiment

Answer 31

Trying to observe earth's motion through the ether, and how it affected the speed of light Two perpendicular beams of light should move through the ether at different rates, by splitting a beam of ligh so they are at 90°, tried to observe this difference

Question 32

Expected results of the M-M experiment

Answer 32

The light was EXPECTED to arrive out of phase with fringes of width w Due to the light travelling parallel to the ether wind should move slower, when the equipment was then rotated through 90° the fringed should shift by 0.4w due to the change in direction relative to the ether wind

Question 33

The actual results of the M-M experiment

Answer 33

The interference shifted by 0.05w, the experiment was repeated but the same results where found. This was a NULL result which disproved the ether and showed the speed of light to be invariant (constant)

Question 34

Inertial frame of reference

Answer 34

A system of objects which are moving at a constant velocity relative to eachother

Question 35

Einsteins two postulates

Answer 35

1. the laws of physics, expressed in equations, have the same form in all inertial frames 2. The speed of light in free space is invariant (contradicts wave theory)

Question 36

Special relativity

Answer 36

Special: no acceleration Relativity: motion is relative to the inertial fram you are in

Question 37

Time dilation

Answer 37

As your speed increase, time moves slower. A moving clock will run slower than a stationary clock t⁰

Question 38

Time dilation equation

Answer 38

t⁰/γ where γ²=1/1-(v²/c²) Equation derived by trig with a light clock on a moving train

Question 39

Proper time

Answer 39

Time recorded in the same inertial frame of reference as the thing you are observing (e.g the clock on the train) shown as t⁰ in equations

Question 40

The relativistic factor

Answer 40

Also known as the Lorentz factor in is γ²=1/(1-v²/c²) γ<1 and will tend to infinity as v approaches c

Question 41

Length contraction

Answer 41

When an objective is moving relative to an observer it's observed length in the direction of motion decreases L⁰>L

Question 42

Proper length

Answer 42

Length recorded by observer stationary relative to the object

Question 43

Length contraction equation

Answer 43

L=L⁰(1-v²/c²)½

Question 44

Why can muons be recorded on the earths surface

Answer 44

Time dilation means the muons experience a shorter time than one a person standing on earth would record Length contraction means the length from the muons frame of reference is contracted when compared to L⁰

Question 45

Relativistic mass

Answer 45

Mass increase with speed The proper mass is the rest mass, when v=0

Question 46

Equation for mass

Answer 46

m⁰/(1-v²/c²)½

Question 47

How does relativistic mass limit velocity of objects

Answer 47

Relativistic mass means no object can travel at light speed, if v=c then the mass of the object would be infinite which isn't possible

Question 48

Energy of a moving particle

Answer 48

Total energy= rest energy+ kinetic energy mc²=m⁰c²+KE This shows energy increases with speed

Question 49

Botozzis Experiment

Answer 49

Electons where accelerated through a p.d and then fired across a known distance to an aluminium plate. An oscilloscope was used to record time for the electron to pass across the distance so velocity could be calculated. This also causes the heating of the aluminium plate so energy of electrons could be calculated

Question 50

Botozzis conclusion

Answer 50

When v² was plotted against kinetic energy the graph was not linear as predicted by ½mv² but curved forming an asymptote so when v is great KE≠½mv²

Question 51

Does W=eV then if ½mv² is wrong

Answer 51

Yes as the increase in temperature of aluminium plate equaled eV mcΔθ=eV