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Physics A Level > 3.3.1 Waves > Flashcards

3.3.1 Waves Flashcards

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1
Q

How do waves transfer energy?

A

Without the transfer of matter.

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2
Q

c (or v) = ?. What is the worded equation?

A

fλ. wave speed = frequency x wavelength.

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3
Q

Define transverse wave.

A

The vibration/oscillation is at 90 degrees (perpendicular) to the wav direction.

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4
Q

Define longitudinal wave.

A

Vibration/ oscillation is parallel to the wave direction.

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5
Q

Give two examples of transverse waves.

A

EM spectrum, S-wave earthquakes.

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6
Q

Give two examples of longitudinal waves.

A

Sound, P-wave earthquakes.

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7
Q

Define the period of a wave.

A

The time to create 1 complete wave.

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8
Q

How is a stationary wave formed?

A

When two waves of the same frequency pass through eachother.

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9
Q

What is a node?

A

The point where the waves cancel and there is no displacement.

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10
Q

What is an antinode?

A

The point where the waves interfere constructively.

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11
Q

What is the simplest standing wave, what is it referred to as and what is the distance between the nodes?

A

Your NAN. (Single loop with a node at each end and an antinode in the middle). It is called the fundamental mode of vibration/ fundamental, distance between nodes are 0.5λ.

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12
Q

What is the next standing wave from the fundamental and what is it called?

A

NANAN, second harmonic.

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13
Q

Give a 6 mark answer for how a standing wave is formed.

A
  • When the crest of the wave on a string arrives at the far end it reverses phase and is reflected, returning as a trough.
  • When it once again reaches the vibrator, it reflects, changes phase and once more becomes a crest.
  • This is further reinforced by a new crest leaving the vibrator, then the amplitude is increased.
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14
Q

What does raising the tension/ shortening the length do?

A

Increases the frequency.

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15
Q

What does lowering the tension/ increasing the length do?

A

Lowers the frequency.

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16
Q

What is polaroid cellulose film used for?

A

To reduce glare from reflections.

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17
Q

How does polaroid cellulose film reduce glare?

A

Reflected light is plane polarised, the light is an EM wave so the E-field is reflected in one particular plane. The crystals in the polaroid absorb these waves so the reflection disappears.

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18
Q

What sort of waves are polarised, why can’t we polarise other waves?

A

Transverse waves can be polarised. Can’t polarise longitudinal waves as they can still oscillate through the crystal structure.

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19
Q

Which waves show the effect of interference?

A

All.

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20
Q

What does interference rely on and what are some examples?

A

Relies on waves constructively and destructively interfering. Eg. patterns on a butterfly wing, car paint wraps, oil on water.

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21
Q

What happens when waves pass through a small gap? How do we increase the effect?

A

Diffraction, more diffraction if gap = λ.

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22
Q

What happens when we pass waves through two gaps close together?

A

Waves overlap and cause bright spots.

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23
Q

Define constructive and destructive interference.

A

Crest meets crest, trough meets trough is constructive. Crest meets trough and creates no displacement is destructive.

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24
Q

Who said light was a particle, what did he call it?

A

Isaac Newton, corpuscle.

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25
Q

Who said light was a wave?

A

Christian Huygen.

26
Q

Who proved wave property of light, how? What do we call the nature of light?

A

Thomas Young in 1801, used double slit experiment. Wave particle duality.

27
Q

What is a coherent wave/ light source?

A

The waves are in step with eachother.

28
Q

What is Young’s double slit equation and what do the letters represent?

A

λ = ws/D. Fringe separation, w. Slit to screen distance, D. Slit separation, s.

29
Q

What are the equations for constructive and destructive interference using SP and nλ?

A

Constructive S1P - S2P = nλ

Destructive S1P-S2P = (n + 1/2)λ

30
Q

How do we order the beams in the diffraction grating experiment?

A

Central = 0 order beam. 1st, 2nd etc. symmetrically outwards from 0.

31
Q

How does diffraction pattern change with λ?

A

Angle of diffraction between each beam and the zero order beam increases with increasing λ.

32
Q

How does diffraction pattern change with slit difference?

A

The angle of diffraction between each beam and the 0 order beam increases with decreasing gap size.

33
Q

What is the equation for diffraction gratings?

A

nλ = dsinθ. θ is angle between zero order and 1st, 2nd etc order.

34
Q

How do you work out the slit separation for a grating of 300 lines/mm?

A

d = 1/N. d = 1/300x10^3

35
Q

Angle of incidence = ?. What law is this?

A

Angle of reflection. Law of reflection.

36
Q

Define refraction.

A

The change in direction of a wave due to its speed. Most commonly seen when a wave passes from one medium to another medium of different optical densities.

37
Q

What is TAGAGA?

A

Towards (normal) Air Glass Away (normal) Glass Air.

38
Q

Where does light bend when travelling from less to more optically dense materials and vice versa?

A

Towards is less to more. Away is more to less.

39
Q

When light is parallel to the normal what happens to refraction?

A

Doesn’t apply, since ray continues along the normal.

40
Q

What is n? What is the equation? Who’s law is this?

A

n is the refractive index. n = SinI/SinR. Snell’s law.

41
Q

Define refractive index.

A

Measure of the bending of a ray of light when passing from one medium to another (relative to a vacuum).

42
Q

When i < C what happens with the refraction?

A

Away from normal.

43
Q

When i = C what happens with the refraction?

A

Refracts along the boundary at 90 degrees to normal.

44
Q

When i > C what happens with the refraction?

A

TIR.

45
Q

If you send light back along the boundary at 90 degrees to the normal what is r?

A

r = C.

46
Q

What is the equation for C?

A

C = sin^-1(1/n)

47
Q

Define C.

A

The critical angle is the angle at which the emergent ray is refracted along the boundary between the two materials (i.e. the angle of refraction is 90 degrees).

48
Q

What are fibre optics and what do we use them for?

A

‘Wire for light’, TIR carries light from one end of the wire to another. Eg. medical endoscopes, fibre optic communication.

49
Q

Where does TIR take place in a fibre optic cable?

A

At the core-cladding boundary.

50
Q

What are the refractive indexes of the core and cladding?

A

Cladding is lower than core.

51
Q

What do we make the core to reduce absorption?

A

Optically clear.

52
Q

Why is cladding needed?

A

To prevent cross talk from one channel to another, prevents damage to the core.

53
Q

What do we do to the core to reduce multipath dispersion?

A

Thin.

54
Q

Why are fibre optics used for high speed data communication?

A 
Immune to EM interference.
No electrical current, no heating.
Lower losses per unit length, allows longer distances between repeater amplifiers.
No corrosion.
Higher bandwidth, more data transmitted.
55
Q

Define progressive wave.

A

Transfers energy from one point to another without transferring material/matter.

56
Q

What is the equation for frequency?

A

f = 1/T

57
Q

With waves of the same amplitude but higher freq. explain the effect on an amp/distance graph.

A

Smaller λ, smaller spread in main peak/more peaks, central peak is higher, because energy conc. over smaller area.

58
Q

Explain how a bright line is formed by the diffraction grating at the 1st order diffraction angle.

A

Light from each slit superpose, light from adjacent slits have a path difference of 1 λ, all waves are in phase, constructive interference.

59
Q

How do you calculate 1st order diffraction angle?

A

sinθ = λ/d

60
Q

How do you calculate highest order observed?

A 
n = d sinθ/λ
n(max) = d sin90/λ

Physics A Level (15 decks)

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