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AQA A-Level Physics - Additional Information > Option Module - Turning Points in Physics (Paper 3) > Flashcards

Option Module - Turning Points in Physics (Paper 3) Flashcards

1
Q

3.12.1 - The discovery of the electron.

A
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2
Q

3.12.1.1 - Cathode Rays

A
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3
Q

What is an electrode?

A

A conductor, through which electricity passes.

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4
Q

What is a cathode?

A

Negatively
charged electrode.

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5
Q

What is an anode?

A

Positively
charged electrode.

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6
Q

What are discharge tubes?

A

Glass chambers with:
- low pressure gas.
- An anode and cathode at opposite ends of the tube.
- High p.d. (voltage) supply.

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7
Q

Are cathode rays made from positive or negatively charged particles?

A

Negative.

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8
Q

Explain how the discharge tube works.

A
  1. electric field between electrodes.
  2. electric field ionises gas particles.
  3. Atoms separated to electrons and positive ions.
  4. Electrons attracted to anode, Positive ions attracted to cathode.
  5. Beam of electrons emitted from cathode (attracted to anode).
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9
Q

In the discharge tube, why do we have a low pressure gas in the chamber?

A

Allows charged particles to travel more freely.

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10
Q

Why does the gas glow in discharge tubes?

A
  1. electrons and ions travel in opposite directions.
  2. low pressure = space for particles to gain large amounts of KE.
  3. collision occurs and they recombine in excited state.
  4. electrons in atoms de-excite and emit visible light photons.
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11
Q

3.12.1.2 - Thermionic emission of electrons

A
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12
Q

How can formation of a cathode ray be made easier?

A

By heating the cathode (thermionic emission).

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13
Q

Why does thermionic emission work?

A
  1. Electrons in heated cathode have more KE.
  2. This is enough energy to leave cathode surface & move to anode.
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14
Q

What are cathode ray tubes designed to do?

A

Fire the emitted electrons from cathode to anode target.

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15
Q

How do we get a tight beam of electrons (cathode ray)?

A

electrons are emitted towards the anode.

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16
Q

What equation can we use to calculate the speed of the electrons in the cathode ray?

A

The equation is derived and explained in notes.

eV = 1/2 x m(e) x v^2.

m(e) = mass of electron.
v = speed of electron.
e = charge of electron.
V = potential difference in the discharge tube.

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17
Q

3.12.1.3 Specific charge of the electron (A-level only)

A
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17
Q

What are the two different methods in determining the specific charge of an electron?

A
  1. Fine beam tube.
  2. Thomson’s crossed fields.
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18
Q

How is a fine beam tube used to determine the specific charge of an electron?

A
  1. electrons accelerated using electron gun.
  2. magnetic force on electron acts perpendicular to motion = centripetal force.
  3. electrons move through fine beam tube, become excited, then de-excite.
  4. Visible light photons are released making path visible, and radius measurable.
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19
Q

Using the fine beam tube experiment to determine specific charge of an electron, what is the equation to calculate the electron specific charge?

A

e/m(e) = 2V / B^2 r^2.

e/m(e) = specific charge.
B = magnetic flux density (in T).
r = radius of path of electron motion.
V = p.d. applied.

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19
Q

How is the Thomson’s crossed fields method used to determine the specific charge of an electron?

A
  1. electrons accelerated using electron gun.
  2. electrons enter perpendicular to both B field and E field.
  3. electrons deflection occurs.
  4. Strength of E and B fields adjusted until electron beam passes undeflected.
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20
Q

In the Thomson crossed fields experiment, what is the equation used to determine the specific charge of an electron?

A

In notes.

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21
Q

Why was Thomson’s determination of specific charge significant?

A

He showed that specific charge was constant.

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22
Q

Compare the specific charge of an electron to that of a hydrogen ion?

A

specific charge of electron is approx 1800 times larger than a proton (hydrogen ion).

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23
Q

3.12.1.4 Principle of Millikan’s determination of the electronic charge, e (A-level only)

A
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24
Q

What was Millikan’s oil drop experiment used to determine?

A

The value of the fundamental or elementary charge, e.

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25
Q

What was the method for Millikan’s Oil drop experiment?

A
  1. Atomised oil drops sprayed into chamber.
  2. Drops are ionised by X-rays.
  3. Drops pass into region between two metal plates (viewed by microscope).
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26
Q

Why are oil drops used instead of water droplets?

A

Oil drops don’t evaporate as quickly.
So mass of drops = constant.

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27
Q

What equation represents the condition necessary for stationary oil drops?

A

QV/d = mg.

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28
Q

How do we get terminal velocity for the falling motion of oil droplets?

A

Turning off the electric field produced.

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29
Q

What are the conditions or assumptions required for the Stokes’ law equation?

A

Object is small.
Object is spherical (with radius r)
Low speed

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30
Q

What is the equation for viscous drag force, F?

A

This is given on data sheet.

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31
Q

What do we equate the equation for the viscous drag force, F, equal to?

A

mg, when at terminal velocity.

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32
Q

When can we use the density?

A

If the mass and radius are unknown, for the sphere.

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33
Q

What was the significance of Millikan’s results?

This includes the quantisation of charge.

A

Each charge droplet had a charge with a value of an integer multiple of 1.6 x 10^-19 C.

This meant charge was quantised and that this was the magnitude of the charge of an electron.

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34
Q

3.12.3 Special relativity (A-level only)

A
35
Q

3.12.3.1 The Michelson-Morley experiment

A
36
Q

What was an ether?

A

This is what permeates the whole universe.

37
Q

How did the ether work?

A

This was an substance that allowed light waves to travel.

38
Q

What were Michelson and Morley trying to test in their experiment?

A

How much the ether slowed slowed down the speed of light.

39
Q

What was used to test Michelson and Morley’s experiment?

A

An Interferometer.

40
Q

What did the interferometer allow?

A

The interference of light rays.

41
Q

Sketch a labelled diagram set up for the Michelson Morley experiment.

A

This is in page 8 of notes.

NOTE: The interferometer was the entire setup.

42
Q

Why was the compensator used in the set-up?

A

Ensure that both beams travel through same glass thickness.

To prevent overlapping of waves.

43
Q

What did Michelson and Morley do with the experiment?

A

Look through telescope to see an interference pattern of fringes.

44
Q

How was bright fringe produced?

A

Where 2 beams arrive in phase.

45
Q

How was dark fringe produced?

A

Where 2 beams arrive out of phase by 180 degrees or Pi radians.

46
Q

What did Michelson and Morley expect to see in their experiment?

A

Turning apparatus through 90 degrees would swap beam directions relative to earth’s absolute motion, shifting patterns.

47
Q

What did Michelson and Morley actually see in their experiment?

A

They were unable to detect fringe shift.

48
Q

What was Michelson and Morley’s conclusion?

A
  • Ether does not exist.
  • Speed of light is invariant in free space.
49
Q

What is a null result?

A

A result or outcome that does not support the initial hypothesis.

50
Q

What is absolute motion?

A

The translation of a body from absolute place into another.

51
Q

3.12.3.2 Einstein’s theory of special relativity

A
52
Q

What is an inertial frame? (or inertial frame of reference).

A

Those which move at constant velocity, not undergoing any acceleration.

53
Q

What is a frame of reference?

A

A set of coordinates used to determine positions and velocities of objects in that frame or stage.

54
Q

Which frames cannot be an inertial frame of reference?

A

A frame that is accelerating or rotating.

55
Q

What is meant by the postulates of special relativity?

A

The assumptions of special relativity.

56
Q

State the 2 postulates (assumptions) of special relativity.

A

speed of light in free space is invariant.
laws of physics have same actions in all inertial frames of reference.

57
Q

3.12.3.4 Length contraction

A
58
Q

What is the proper length?

A

The length measured by observer, who is at rest relative to the object.

59
Q

What is the symbol for proper length?

A

lo.

60
Q

What is the equation that links the proper length to the length measured in another inertial frame?

A

It is on page 10.

61
Q

3.12.3.5 Mass and Energy

A
62
Q

What is larger - relativistic mass of moving object or rest mass?

A

Relativistic mass.

63
Q

What is the equation that links the relativistic mass and rest mass?

A

It is on page 10.

64
Q

Sketch a graph of relativistic mass against speed.

A

Graph on page 10.

65
Q

What is the equation linking total energy to relativistic mass?

A

Page 11.

66
Q

How could you work out the kinetic energy if you know the total energy and the rest mass?

A

Equation on page 11.

67
Q

Sketch a graph of KE against speed.

A

Page 11.

68
Q

What was Bertozzi’s experiment?

A

Measure speed of electrons with different kinetic energies.

69
Q

How did Bertozzi accelerate the electrons?

A

Particle accelerator was used to emit the electrons at various KE.

70
Q

How did Bertozzi measure the speed of the electrons?

A

Time: electrons released in pulses. Time to travel between detectors measured on oscilloscope.

Distance: distance between the detectors.

Speed = distance/time.

71
Q

How did Bertozzi know the KE?

A
  • electrons collide with target.
  • KE is transferred to heat.
72
Q

In Bertozzi’s experiment, how do you calculate the KE of one electron?

A

mc(change in temp) / n.

n = no. of electrons in one pulse.

73
Q

What was Bertozzi’s conclusion?

A

Values were very close to those predicted by Einstein’s theory of special relativity.

= valid experiment.

74
Q

3.12.3.3 Time Dilation

A
75
Q

What is proper time?

A

The amount of time passed, experienced by the stationary observer.

76
Q

What is the symbol for ‘proper time’?

A

to.

o is the subscript.

77
Q

What is the equation that links proper time with the time measured in another inertial frame?

A

Equation on page 9.

v = velocity at which stationary observer is travelling.

78
Q

What is observed for muons travelling from the upper atmosphere to a detector compared to what was expected without special relativity?

A

Cosmic rays create muons in upper atmosphere.

Muons travel at speed of 0.995c towards earth.

79
Q

How is the observation of muons evidence for time dilation and special relativity?

A

Muons take longer than 2.2 microseconds to decay.

So it can reach earth.

80
Q

3.12.2.1 Newton’s corpuscular theory of light

A
81
Q

3.12.2 Wave-particle duality (A-level only)

A
82
Q

Describe Newton’s corpusclar theory of light.

A

A light ray was composed of a stream of tiny particles, called corpuscles.

83
Q

How did newton’s corpuscular theory of light explain reflection?

A

Corpuscles bounce of mirror (no loss of speed).

Normal component of velocity is reversed. Parallel component of velocity is unchanged.

Components of velocity - unchanged, so angle i = angle r.

84
Q

How did newton explain refraction?

A
  • Light ray is refracted.
  • corpuscles are attracted into substance.
  • perpendicular component velocity increases in substances.
85
Q

What was Huygen’s theory?

A

The wave theory of light.

86
Q

How did Huygen explain refraction using his theory?

A

Light waves travelled slower in a more optically dense medium than in air.

87
Q

Why was Newton’s corpuscular theory of light preferred over Huygen’s wave theory of light?

A
  • Speed of light couldn’t be measured at that time.
  • Newton had a stronger reputation.
  • Wave theory was in terms of longitudinal waves, and couldnt explain polarisation.

AQA A-Level Physics - Additional Information (16 decks)

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