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OCR A-level Physics A > 4.4 Waves > Flashcards

4.4 Waves Flashcards

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1
Q

What is a wave?

A

A repeated vibration which transfers energy from one point to another without transferring matter.

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2
Q

What’s the difference between a progressive wave and a stationary wave?

A

A progressive wave transfers energy from one point to another without transferring matter, whereas a stationary wave has no net energy transferred from one point to another.

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3
Q

What is displacement?

A

How far a wave has travelled from its equilibrium position.

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4
Q

What is amplitude?

A

A wave’s maximum displacement from its equilibrium position.

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5
Q

What is wavelength?

A

The length of one compete wave. Wavelength can be measured as the distance between consecutive peaks.

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6
Q

What is a wave’s time period?

A

The time taken for one complete wave to pass a point.

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7
Q

What is a wave’s phase difference?

A

A measure of how much one wave is shifted relative to another wave, measured in degrees or radians.

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8
Q

What is frequency?

A

The number of complete waves which pass a point in a second.

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9
Q

When does reflection occur?

A

When a wave hits a boundary between two materials, bouncing off the surface in a new direction.

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10
Q

When does refraction occur?

A

When waves enter a new medium, causing them to change speed and direction.

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11
Q

What is polarisation?

A

A process affecting waves where their vibrations are restricted to a single plane perpendicular to their direction of energy transfer.

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12
Q

Polarisation can only occur with what kind of wave: transverse or longitudinal?

A

Transverse

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13
Q

What is diffraction?

A

The spreading out of waves when they go through a gap, or past the edge of a barrier.

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14
Q

How wide does the wavelength have to be for diffraction to become significant?

A

Comparable to the gap width.

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15
Q

What is wave intensity?

A

A measure of the energy that a wave transfers through a unit area perpendicular to its direction of travel per second.

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16
Q

The “brightness” of light and “loudness” of sound refer to which technical term of a wave?

A

Intensity

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17
Q

Intensity is directly proportional to… what?

A

Amplitude²

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18
Q

Are electromagnetic waves transverse or longitudinal?

A

Transverse.

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19
Q

Are electromagnetic waves progressive or stationary?

A

Progressive.

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20
Q

Name all of the electromagnetic waves in order of increasing wavelength and decreasing frequency.

A

Gamma rays
X-rays
Ultraviolet
Visible light
Infrared
Microwaves
Radio waves

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21
Q

What is the typical wavelength of a radio wave?

A

10³

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22
Q

What is the typical wavelength of a microwave?

A

10⁻²

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23
Q

What is the typical wavelength of an infrared wave?

A

10⁻⁵

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24
Q

What is the typical wavelength of visible light?

A

0.5x10⁻⁶

25
Q

What is the typical wavelength of ultraviolet?

A

10⁻⁸

26
Q

What is the typical wavelength of x-rays?

A

10⁻¹⁰

27
Q

What is the typical wavelength of gamma rays?

A

10⁻¹²

28
Q

What can be used to polarise light?

A

Polarising filters

29
Q

What can be used to polarise microwaves?

A

Metal Grilles

30
Q

How many polarising filters would you need t completely block light, and how would you position them?

A

Two polarising filters at right angles to one another would completely block light.

31
Q

What is the angle of incidence?

A

The angle between a ray incident on a surface and the line perpendicular to the surface

32
Q

What is the angle of reflection?

A

The angle between a reflected ray off a surface and the line perpendicular to the surface

33
Q

If a wave passes into a denser medium, does it speed up or slow down?

A

Passing into a denser medium causes the wave to slow down.

34
Q

When a wave slows down, does it refract towards or away from the normal line?

A

Towards the normal line.

35
Q

When a wave speeds up, does it refract towards or away from the normal line?

A

Away from the normal line.

36
Q

What is the refractive index and how is it calculated?

A

The refractive index (n) is the ratio light’s speed in a vacuum (c) to its speed in a material (v).
n = c / v

37
Q

What is Snell’s law, what is the formula and what do the symbols mean?

A

Snell’s law links the angles of incidence and refraction to the refractive indices of two materials.
n₁ / n₂ = sinθ₂ / sinθ₁
θ₁ = angle of incidence
θ₂ = angle of refraction
n₁ and n₂ = refractive indices of each material

38
Q

What is the name given to the angle of incidence at which light will reflect off a boundary rather than refracting in the medium?

A

The critical angle

39
Q

What two conditions are required for Total Internal Reflection to occur?

A
  1. The light must travel from a denser to a less dense medium.
  2. The angle of incidence must be greater than the critical angle for the two media.
40
Q

How do you calculate the critical angle for two media? Give the equation that is not in the formula book.

A

sin θ = n₂ / n₁
Where n₁ is the refractive index of the denser medium and n₂ is the refractive index of the less dense medium.

41
Q

What is the principle of superposition?

A

When two waves meet at a point, the resultant displacement of the wave at that point is equal to the sum of the displacements of the individual waves.

42
Q

What does it mean for two waves two be coherent?

A

They have the same frequency and wavelength, and a fixed phase difference.

43
Q

What is the difference between path difference and phase difference?

A

Path difference is the difference in distance that two waves have travelled in terms of wavelength (units of length).

Phase difference is the difference in the point in the cycle of two waves as a proportion of a full wave cycle.

44
Q

How is phase difference related to constructive interference?

A

Constructive interference occurs when the phase difference between the waves is an integer multiple of 2𝜋 radians (360°), meaning the waves are in phase and their amplitudes add up.

45
Q

How is phase difference related to destructive interference?

A

Destructive interference occurs when the phase difference between the waves is an odd multiple of 𝜋 radians (180°), meaning the waves are out of phase and their amplitudes subtract, leading to cancellation.

46
Q

At what phase differences do constructive and deconstructive interference occur?

A

A phase difference of 0 or 2𝜋 radians (360°) leads to constructive interference, while a phase difference of 𝜋 radians (180°) leads to destructive interference.

47
Q

How are stationary waves formed?

A

Through superposition, when two coherent waves (with the same wavelength and frequency), but travelling in opposite directions, superpose. These conditions are often met when a wave is reflected back upon itself.

48
Q

What is a node?

A

A point of destructive interference, when two waves cancel each other out which results in no movement or zero amplitude.

49
Q

What is an antinode?

A

Points of constructive interference where the waves reinforce each other, creating points of maximum movement or amplitude.

50
Q

True or false: Stationary waves transfer energy.

A

False. Unlike progressive waves, stationary waves don’t transfer energy.

51
Q

Give a similarity between stationary waves and progressive waves.

A

Both have a wavelength, frequency and amplitude.

52
Q

Is an antinode or a node formed at a closed end of an air column?

A

Node

53
Q

Is an antinode or a node formed at a open end of an air column?

A

Antinode

54
Q

Is each end of a vibrating string a node or an antinode?

A

A node.

55
Q

What is the separation between adjacent nodes (or antinodes) equal to in terms of the wavelength of the progressive wave (λ).

A

λ / 2

56
Q

What is a harmonic?

A

A point where the stationary waveform doesn’t change because the wavs in each direction are reinforcing each other.

57
Q

What’s the wavelength of the first harmonic?

A

λ / 2

58
Q

How many nodes and antinodes does the first harmonic have, and where are they positioned?

A

Nodes - 2 (1 at either end)
Antinodes - 1 (in the middle)

59
Q

What is the fundamental frequency?

A

The lowest frequency of vibration for a given arrangement.

OCR A-level Physics A (7 decks)

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