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AS Physics 2 > Section 3: Waves > Flashcards

Section 3: Waves Flashcards

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1
Q

True or False: Amplitude can have a negative value but displacement can’t.

A

False, other way round

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2
Q

Describe what is meant by the phase of a wave.

A

A measurement of the position of a certain point along the wave cycle

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3
Q

Explain what is meant by the phase difference of two waves.

A

The amount by which one wave lags behind another

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4
Q

Give the formula to calculate wave speed.

A

C=d/t

Wave speed equals distance/time

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5
Q

What is the difference between transverse and longitudinal waves?

A

In transverse waves, the direction of displacement of the particles is at right angles to the direction of energy transfer (perpendicular). Whereas in longitudinal waves the direction of displacement of the particles is along the direction of energy transfer (parallel)

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6
Q

What happens when you put two polarising filters at right angles in front of a beam?

A

Light is blocked as the filters block all directions of oscillations

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7
Q

What happens to unpolarised light when it is reflected from the surface of water?

A

It is partially polarised-some of the vibrations of the reflected light are in the same direction

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8
Q

How does a wave transfer energy through a medium?

A

By causing the particles in the medium to oscillate

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9
Q

What is wavelength?

A

The length of one whole wave oscillation

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10
Q

What is displacement?

A

The distance a point has moved from its original position in a given direction

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11
Q

What is amplitude?

A

The maximum magnitude of the displacement

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12
Q

What is the period?

A

The time taken for one whole wave cycle

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13
Q

How does a wave transfer energy through a medium?

A

By causing the particles in the medium to oscillate

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14
Q

Describe what is meant by:

a) The phase of a wave.
b) The phase difference of two waves

A

a) A measurement of position of a centre point along the wave cycle
b) The amount by which one wave lags behind another

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15
Q

How would you calculate the frequency of a wave, given its period?

A

Frequency=1÷period

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16
Q

Given an example of a longitudinal wave.

A

Sound waves or earthquake-shock waves (P-waves)

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17
Q

Given an example of a transverse wave.

A

Electromagnetic or water waves

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18
Q

What happens when you put two polarising filters at right angles to one another?

A

No light gets through

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19
Q

What happens to unpolarised light when it is reflected from the surface of water?

A

It is partially polarised

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20
Q

Explain how polaroid sunglasses reduce glare.

A

Light is partially polarised in some materials. Polaroid sunglasses block out light in the direction in which the light is partially polarised, but let through light vibrating in other directions. This reduces glare without hindering visibility

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21
Q

Other than polarised sunglasses, give one example of how polarised waves are relevant to everyday life

A

Reducing reflections in photography/ aligning TV and radio receivers

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22
Q

What does the principle of superstition say?

A

When two or more waves meet, the resultant displacement equals the vector sum of the individual displacements

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23
Q

Describe constructive interference.

A

When two waves pass through each other and their displacements combine to make a displacement with greater magnitude

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24
Q

What is total destructive interference?

A

When two waves pass through each other and their displacements cancel each other out completely

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25
Q

What is the phase difference of two points on a wave?

A

The phase difference of two points on a wave is the difference in their positions in the wave cycle

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26
Q

Give the three possible units for phase difference.

A

Degrees, radians or fractions of a cycle

27
Q

When are two points on a wave exactly out of phase?

A

When their phase difference is an odd multiple of 180 degrees (radians or half a cycle)

28
Q

What does it mean for two waves to be in phase?

A

Two waves are in phase if they have a phase difference of 0 degrees or a multiple of 360 degrees

29
Q

How is a stationary wave formed?

A

When two progressive waves are travelling in opposite directions with the same frequency and the same amplitude, their superstition creates a stationary wave

30
Q

Does a stationary wave transfer energy?

A

No

31
Q

Describe what a resonant frequency of a wave is.

A

A resonant frequency of a string is a frequency at which a stationary wave is formed because an exact number of waves are produced in the time it takes for a wave to get back to the end of the string again

32
Q

What would happen to the frequency of the first harmonic of a string if the string was replaced with a heavier string? Assume everything else is kept constant.

A

The resonant frequency of the string would decrease if a heavier string was used, as the mass per unit length would increase. The decrease in frequency is because waves travel slower down a heavier string

33
Q

A vibration transducer is used to create stationary waves on a string. Explain why increasing the length of the vibrating string causes frequency of the first harmonic to decrease.

A

The harmonic frequencies correspond to the number of half wavelengths on a string. If the length of the string is increased, the wavelength of the resonant frequency also increases. c= frequency x wavelength

34
Q

What type of waves diffract?

A

All waves

35
Q

What size of gap would you expect to produce the most diffraction?

A

Roughly the same as the wavelength of the wave being diffracted

36
Q

What is monochromatic light?

A

Light that is made up of only one frequency of light

37
Q

What sort of interference is responsible for the bright fringes on a diffraction pattern produced by laser light passing through a single slit?

A

Constructive interference

38
Q

Describe the diffraction pattern produced when white light is shone through a single narrow slit.

A

A white central maximum with outer fringes that are spectra

39
Q

What of property of laser light means that it will produce a cleaner diffraction pattern than white light? Explain your answer.

A

It’s monochromatic so all the light is dispersed in a clear diffraction pattern

40
Q

Explain what would happen to the central maximum of a single-slit diffraction pattern if the slit width was decreased.

A

If the width of the single-slit decreased the amount of diffraction would increase. This would cause the central maximum to get wider and less intense

41
Q

Explain what effect increasing the wavelength of a light source would have on the width of the central maximum of its single-slit diffraction pattern.

A

if the wavelength of the incident light was increased, then the amount of diffraction would increase. This would cause the central maximum to get narrower and more intense

42
Q

Explain what happens in terms of photons when the intensity of a monochromatic light source is increased

A

Intensity is the power per unit area. Monochromatic light is made up of photons which all have equal energies. This means that an increase in intensity results in more photons hitting a unit area in a given time

43
Q

What does it mean for two wave sources to be coherent?

A

If the waves emitted by the two sources are of equal wavelength, frequency and have a fixed phase difference between them

44
Q

What must be true of two wave sources if they produce a clear, standard two-source interference pattern?

A

They must be coherent

45
Q

What is meant by the path difference of two waves?

A

The amount by which the path travelled by on wave is longer than the path travelled by another wave

46
Q

At what path differences will you see constructive interference?

A

You can see constructive interference when the path difference is an integer

47
Q

How can you create two coherent sources of sound waves?

A

Have one amplifier attached to two speakers

48
Q

Explain how Young’s double slit experiment suggested that light was a wave.

A

It showed that light could diffract and interfere, both of these are wave qualities

49
Q

Why is it often better to use a diffraction grating instead of a double-slit formula?

A

The fringes produced in a diffraction grating experiment are much sharper than those produced with a double-slit set-up

50
Q

What’s the zero order line of a diffraction grating experiment?

A

A line of maximum brightness at the centre of the diffraction patter. It’s in the same direction as the incident beam

51
Q

What would happen to the interference pattern produced if you increased the wavelength of light transmitted through a diffraction grating?

A

The pattern would spread out

52
Q

What would happen to the interference pattern produced if the light was transmitted through a coarser diffraction grating?

A

The pattern would be less spread out

53
Q

Describe the appearance of the zero and first orders of interference pattern for white light.

A

The zero order line is a white line. The first order line is a spectrum of colours

54
Q

Why are spectra formed when white light passes through a diffraction grating?

A

White light is made up of a range different wavelengths. These spread out by different amounts when they pass through the diffraction grating crating a spectrum

55
Q

Explain how X-ray crystallography works.

A

X-rays are fired at a crystal lattice, which acts as a diffraction grating. The diffraction patterns produced are used to analyse atomic structure

56
Q

What is the refractive index of a material?

A

It’s a measure of the optical density of the material, given by the ratio of the speed of light in a vacuum to the speed of light in the material

57
Q

In what way will light bend if it passes at an angle into a medium with a higher refractive index than the material it just left?

A

It will bend towards the normal

58
Q

What is meant by the critical angle of a boundary of two materials?

A

The critical angle of a boundary is the angle of incidence at which the angle of refraction is 90 degrees

59
Q

State two functions of the cladding of optical fibres

A

Cladding has a lower optical density than the optical fibre so it allows total internal reflection. It is also used to protect the fibre from scratches and damage which could let light escape

60
Q

Explain how absorption in optical fibres causes signal degrading.

A

Absorption is where the fibre material absorbs some of the energy from the signal, which reduces the amplitude of the signal, leading to signal degradation

61
Q

Name two kinds of dispersion which can cause pulse broadening in optical fibres and explain what cause them.

A
  • Modal dispersion is caused by light rays taking different paths downs the fibre, some of which are faster than others. This is caused by light entering the fibre at a range of angles.
  • Material dispersion is caused by different wavelengths taking different times to travel through the fibre
62
Q

Explain why signal degradation is a problem when using optical fibres to send information.

A

It can result in a loss of information

63
Q

Describe and explain three ways to prevent signal degradation in optical fibres.

A

Using a single-mode fibre reduces modal dispersion as light is restricted to a very narrow path. Using monochromatic light prevents material dispersion as there is no variance in wavelength. Using a signal booster to regenerate and amplify the original signal regularly prevents losses from absorption or dispertion

AS Physics 2 (9 decks)

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