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physics a-level paper 2 > Topic 5: Waves and Particle Nature of Light > Flashcards

Topic 5: Waves and Particle Nature of Light Flashcards

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1
Q

What is amplitude?

A

Amplitude is a wave’s max displacement

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2
Q

What is frequency?

A

Frequency is the number of complete oscillations passing through a point per second.

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3
Q

What is time period?

A

Time taken for one full oscillation

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4
Q

What is wavespeed?

A

The distance travelled by the wave per unit time

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5
Q

What is wavelength?

A

The length of one whole oscillation.

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6
Q

What are the properties of oscillations in longitudinal waves?

A

In longitudinal wave, oscillations are parallel to the direction of energy transfer.
They are
- Made of compressions and rarefractions

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7
Q

What are the properties of oscillations in transverse waves?

A

In transverse waves, oscillations are perpendicular to direction of transfer

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8
Q

What is phase of a wave?

A

Position of a certain point in a wave cycle.

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9
Q

What is phase difference in waves?

A

How much a particle/wave lags behind another particle/wave.

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10
Q

What is path difference?

A

Path difference is the difference in distance travelled by 2 waves.

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11
Q

What is superposition?

A

Superposition is when displacements of 2 waves combine as they pass each other.
The resultant displacement is the vector sum of both displacements.

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12
Q

What is a wavefront?

A

Wavefront is a surface which is used to represent the points of a wave which have the same phase.

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13
Q

What is coherence?

A

Coherent light source has the same frequency and wavelength.

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14
Q

What is a wavefront?

A

A wavefront is a surface used to represent points of a wave which have the same phase.

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15
Q

What is constructive interference?

A

Constructive interference is when 2 waves superpose and their amplitudes add together

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16
Q

When does constructive interference occur?

A

Occurs when two waves are in phase and superpose.

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17
Q

What is destructive interference?

A

Destructive interference is when two waves superpose and their amplitudes cancel out, decreasing amplitude of resulting wave.

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18
Q

What does it mean when 2 waves are in/out phase?

A

In phase means when 2 waves have
- the same frequency and wavelength.
- phase difference is a multiple of 2π

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19
Q

What does a standing/stationary wave do?

A

It stores energy.

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20
Q

How is a standing/stationary wave formed?

A

When 2 waves of same frequency/wavelength/amplitude are travelling in opposite directions and superpose.

E.g waves in a contained box, one reflects and interferes with initial wave

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21
Q

What happens where standing waves meet in phase/ anti-phase?

A

When waves meet in phase
- Constructive interference occurs
- Anti-nodes are formed; regions of max displacement

When waves meet out of phase
- Destructive interference occurs
- Nodes are formed; regions of 0 displacement

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22
Q

How to calculate speed of a transverse wave on a string?

A

v = √T/μ

T = tension in string
μ - mass/unit length

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23
Q

What is definition and formula for intensity?

A

Intensity is power/unit area

I=P/A

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24
Q

What is refraction?

A

Refraction is when a light ray enters a new medium with different density leading to a change in speed and change direction.

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25
Q

What does the refractive index of a material mean and what is formula?

A

Measurement of how much the material slows down light passing through it.

n = c/v
Higher refractive index = more optically dense

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26
Q

What happens when the new medium is more/less optically dense?

A

When medium is more dense;
- Light ray slows down; bends towards the normal

When medium is less dense
- Light ray speeds up; bends away from normal

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27
Q

What is the critical angle?

A

Critical angle is the angle of incidence causes angle of refraction to be exactly 90° and reflected along the boundary.

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28
Q

How can you calculate critical angle when one medium is air?

A

Use formula sinC = 1/n
C - Critical angle
n

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29
Q

What is total internal reflection?

A

Total internal reflection is when light ray in the medium is reflected at the same angle off the boundary.

30
Q

When does total internal reflection occur?

A

Occurs when angle of incident > critical angle

31
Q

What are the 2 types of lenses?

A

Converging - convex shaped lens; curved outwards; cause parallel light rays to converge to focal point

Divergent - concave shaped lens; curved inwards; light rays diverge from a point

32
Q

What is the principle focus?

A

In converging
- where light rays meet
In diverging
- where image appears to come from

33
Q

What is the focal length?

A

Focal length is the distance from the centre of the lens to the principle focus

34
Q

What is the power of a lens?

A

Measure of lens’ ability to bend light.
Converging - positive value
Diverging - negative value

35
Q

How can you work out the power of a lens?

A

Power = 1/focal length

36
Q

How to draw ray diagrams?

A
  1. Draw a line parallel to principle axis then draw connecting line through focal point
  2. Draw a line through centre of lens
37
Q

When is a real/virtual image produced in ray diagrams?

A

Real - when the rays meet at the other end of the principal axis
Virtual - when rays meet at same end of principal axis

38
Q

When is a magnified/shrunk image produced in a ray diagram?

A

Magnification - when the image is taller than the object
Shrunk - when the image is shorter than object

39
Q

What is a real/virtual image?

A

Real - Image that can be projected onto a screen as light rays reach image location
Virtual - Image that can’t be projected onto a screen.

40
Q

How can you use the distances of images in a ray diagram to calculate power?

A

1/u + 1/v = 1/f

41
Q

When does polarisation occur?

A

Polarisation occurs when particles are only allowed to oscillate in one of the directions perpendicular to direction of wave propagation.

42
Q

Which directions can a transverse wave be oscillated in?

A

Transverse waves can be polarised horizontally, vertically or any direction in between.

43
Q

Why can longitudinal waves not be polarised?

A

Longitudinal waves oscillate parallel to direction of wave transfer; polarisation requires wave to oscillate perpendicular to propagation.

44
Q

How can light be polarised?

A

Light can be polarised by passing it through polarising filter.

45
Q

What is diffraction?

A

Diffraction is the spreading out of waves when they pass a gap.

46
Q

What is Huygens’ construction?

A

Huygens’ construction states that every point on a wavefront is a point source to secondary wavelets.

47
Q

What does the amount of diffraction depend on?

A

Diffraction increases as the wavelength gets closer to length of gap. Greatest amount of diffraction occurs when gap = wavelength

48
Q

What is a diffraction grating?

A

Diffraction grating is a slide containing equally spaced slits close together.

49
Q

What happens when a monochromatic light/laser is lit through a diffraction grating?

A

Pattern of narrow bright fringes produce on a screen.

50
Q

What is the diffraction grating equation?

A

dsin = nλ

d - distance between slits
θ - angle to normal made by maximum
n - order
λ - wavelength

51
Q

What is an interference in waves?

A

Interference is a boundary between 2 materials.

52
Q

What 2 things happen at an interference?

A

Transmission
- When they pass into the next material
Reflection
- Hits the boundary but does not pass through, reflects and stays in original medium

53
Q

How to know if transmission or reflection will occur?

A

Transmission occurs when densities of materials are similar
Reflection occurs when densities of materials are different

54
Q

What is the pulse-echo technique used with?

A

Pusle-echo technique is used with ultrasound waves (>20kHz) for imagining of objects

55
Q

Why are ultrasound waves used in pulse-echo technique?

A

Non-invasive
- no ionising radiation; safer to perform x-rays
High freq
- Above human-hearing; high freq = better resolution

56
Q

What does the pulse-echo technique rely on?

A

It relies on the fact that waves are reflected when they meet boundaries of different material.

57
Q

How does pulse-echo technique work?

A
  • Short pulses of ultrasound waves transmitted into target.
  • Pulse travels inside target until some of pulse is reflected back; amount of reflection depends on difference in densities; higher diff, higher reflection
  • Reflected waves are detected
  • Intensities of reflected waves used to determine structure of target;
    time taken for reflected waves to return is used to determine position in the target.
58
Q

What determines the position of objects in the target in pulse-echo technique?

A

Position is determined by the time taken for reflected wave to return.

59
Q

What determines the structure of the target?

A

Structure is determined by the intensities of reflected waves.

60
Q

What 2 things will decrease the resolution in pulse-echo technique?

A
  • If duration of pulses is too long; they will likely overlap; amount of information obtained will decrease
  • If wavelength of waves used increases, less fine details, less information obtained
61
Q

What does the photon model state?

A

EM waves travel in discrete packets called photons.

62
Q

What does the wave model state?

A

Wave model states EM radiation can be described as transverse waves.

63
Q

How to calculate photon energy?

A

E = hf

64
Q

What is the photoelectric effect?

A

When photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it.

65
Q

What is the threshold frequency?

A

Threshold frequency is the minimum frequency of light required for a electron to be emitted from the surface of a metal.

66
Q

How are photoelectron emitted?

A

Photoelectrons are emitted as they absorb a photon and gain enough energy to leave the surface.

67
Q

What is the work function of a metal?

A

Work function of a metal is the minimum energy required for electrons to be emitted.

68
Q

Photoelectric equation

A

E = hf = ϕ +KEₘₐₓ

69
Q

What does increasing the intensity of light do to photoelectric emission?

A

It increases photons released; increases number of photoelectrons released

70
Q

What happens to electrons which are deeper in the metal during photoelectric emission?

A

They lose some energy through collision with metal lattice; will have lower kinetic energy

71
Q
A

physics a-level paper 2 (7 decks)

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