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AS-Level Physics > Waves > Flashcards

Waves Flashcards

1
Q

What is a wave?

A

A mechanism that allows energy to be moved from one place to another.

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2
Q

What is a transverse wave?

A

A wave which oscillates perpendicular to the direction of propagation and energy transfer.

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3
Q

What is a longitudinal wave?

A

A wave which oscillates parallel to the direction of propagation and energy transfer.

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4
Q

Give an example of a longitudinal wave.

A

Sound

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5
Q

What is the main difference between transverse and longitudinal waves?

A

Transverse waves can be polarised.

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6
Q

What is wavelength?

A

The distance between adjacent troughs.

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7
Q

What is frequency?

A

The number of waves passing a fixed point every second.

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8
Q

What is amplitude?

A

The distance between the centre line of the wave and the top of the crest.

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9
Q

What is the intensity of a wave?

A
  • The energy deposited per second per metre squared.

- Power deposited per metre squared.

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10
Q

What is the intensity of a wave proportional to?

A

Amplitude squared

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11
Q

What is phase difference?

A

The fraction of one cycle between two vibrating points.

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12
Q

How can phase difference be expressed?

A

Wavelength or angle

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13
Q

What is the plane of polarisation?

A

The plane of oscillation of the particles that make up the wave.

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14
Q

What is the plane of polarisation for an EM wave?

A

The plane in which the electric field component vibrates.

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15
Q

What type of waves are slant polarised?

A

VHF (FM) radio waves

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16
Q

What is needed to form and stationary wave?

A

Two waves of the same type travelling towards each other that have the same frequency and amplitude.

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17
Q

What is an antinode?

A

The maximum displacement of the envelope.

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18
Q

What is a node?

A

Where the displacement of the envelope is zero.

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19
Q

What is a wavefront?

A

The line drawn along the crests of waves.

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20
Q

What is a ray?

A

A line drawn perpendicular to the wavefronts showing the direction of the wavefronts.

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21
Q

What two rules are always observed when reflecting at a plane mirror?

A
  • angle of incidence = angle of reflection

- The incident and reflected ray are in the same plane.

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22
Q

What is the main use for mirrors reflecting light at 45°?

A

A periscope

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23
Q

What are the three properties of an image formed in a plane mirror?

A
  • The image is virtual.
  • The image is the same distance behind the mirror as the object is in front.
  • The image is laterally inverted.
24
Q

What is refraction?

A

The bending of a ray as it passes from one material into another and changes speed.

25
Q

What is refraction?

A

The bending of a ray as it passes from one material into another and changes speed.

26
Q

What is Snell’s Law?

A

sini/sinr = 1n2 = velocity in material 1 / velocity in material 2 = n2/n1

27
Q

What does 1n2 represent?

A

The relative refractive index from material 1 into material 2.

28
Q

What does 1n2 also equal?

A
  • 1 / 2n1

- velocity in material 1 / velocity in material 2

29
Q

What is absolute refractive index?

A

The relative refractive index between a vacuum and the material.

30
Q

What is the critical angle?

A

The angle of incidence for which the angle of refraction is 90°.

31
Q

What happens if the critical angle is exceeded?

A

Total internal reflection occurs.

32
Q

What is Snell’s Law at the critical angle?

A

sinic = n2/n1 = velocity in material 1 / velocity in material 2

33
Q

What is Snell’s Law at the critical angle?

A

sinic = n2/n1 = velocity in material 1 / velocity in material 2

34
Q

What are the two main problems with basic fibre optics?

A
  • If another material comes into contact with the fibre the boundary is no longer glass-air so the critical angle is changed meaning light can escape.
  • If two glass fibres touch there is no boundary meaning light can travel between the two fibres.
35
Q

How is multipath dispersion prevented?

A

Cladding made of a second layer of glass with a lower refractive index is used.

36
Q

What are the two types of fibre optic bundles used for an endoscope?

A
  • Coherent bundle

- Incoherent bundle

37
Q

What type of bundle is used in an endoscope to carry light into the patient?

A

Incoherent bundle

38
Q

What type of bundle is used in an endoscope to carry light out of the patient?

A

Coherent bundle

39
Q

What is the resultant wave displacement of two waves arriving at a point?

A

The vector sum of the individual wave displacements.

40
Q

When are waves coherent?

A

If they have the same frequency or wavelength and a constant phase relationship.

41
Q

What is diffraction?

A

The bending of a wavefront as it passes through a gap or close to the edge of an object.

42
Q

What are the two types of wave interference?

A

Constructive and destructive

43
Q

How is the maximum constructive interference of a laser light calculated?

A

λ = ws / D

w = separation in maxima 
s = slit separation
D = distance from slits to screen
44
Q

How is the width of the central maxima calculated from a single slit?

A

w = 2λD / b

b = slit width
w = central fringe width
45
Q

How is the n order maxima of a diffraction grating calculated?

A

dsinθn = nλ

46
Q

When are two polarising filters “crossed”?

A

When the transmitted energy is at a mimimum.

47
Q

What is the period of a wave?

A

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

48
Q

How is phase difference calculated in radians?

A

2πd/λ

49
Q

What is superposition?

A

When two waves the total displacement is equal to the sum of the individual displacements.

50
Q

How is a microwave used to demonstrate wave properties?

A
  • Moving a receiver away shows that they become weaker.
  • Using a metal plate shows they can be reflected.
  • Using a slit shows how a larger gap reduces diffraction.
  • Using a double slit can show interference.
51
Q

How is the distance between two adjacent nodes calculated?

A

0.5λ

52
Q

When does a light ray bend towards the normal?

A

When going into the more refractive substance

53
Q

How is the refractive index of a substance calculated?

A

sini/sinr

54
Q

What is n1sini equal to?

A

n2sinr

55
Q

From double slit interference, what does a bright fringe show?

A

The light waves from each slit are in phase.

56
Q

From double slit interference, what does a dark fringe show?

A

The two light waves are 180 out of phase

57
Q

How wide is the central fringe of single slit diffraction compared to the outer fringes?

A

It is twice as wide

AS-Level Physics (4 decks)

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