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Higher physics > Waves > Flashcards

Waves Flashcards

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1
Q

What is refraction

A

Refraction is the change in velocity of light when it passes from one medium to another.
If light is incident on a boundary at an angle to the normal other than 90 degrees it will also change direction.

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1
Q

When light travels from a less dense to a more dense material the ray moves […]

A

towards the normal

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2
Q

When light travels from a more dense to a less dense material the ray moves […]

A

away from the normal.

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3
Q

What is absolute refraction index (refractive index)

A

The absolute refraction index, n, of a material is defined as the ratio of the speed of light in a vacuum (c) to the speed of light in the medium (v).

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4
Q

What is the refractive index of a vacuum and of air?

A

1

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5
Q

For any media other than air or a vacuum what is true about the refractive index, n?

A

N is always greater than 1 and has no units (no units for all media)

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6
Q

As refractive index increases what happens?

A

the change in speed and direction of light as it passes from air into the medium increases.

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7
Q

The denser a material the greater the…

A

refractive index

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8
Q

does refractive index change depending on if the light moves from air into the medium or the medium into air?

A

No, the refractive index is the same whether the light moves from air into the medium or the medium into air.

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9
Q

State Snell’s law

A

Snell’s law states:

(n2/n1) = (sin01/sin02)

where n1 and n2 are the refractive indices of the two media.

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10
Q

When one medium is air what happens to the snells law relation ship

A

Since air has a refractive index of 1 the relationship becomes:

(n2/1) = (sin01/sin02)

or as given on the formula sheet:
n = sin01/sin02

where n = refractive index of medium
sin01 angle in air
sin02 angle in medium

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11
Q

What does refractive index of a medium depend on

A

frequency of light, refractive index increases with the frequency of light.

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12
Q

Why does a prism split white light into its spectrum of colour

A

because the prism medium has a different refractive index for each colour of light.

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13
Q

Why does a prism refract violet light more than red light?

A

As violet has a higher frequency than red light, the refractive index for the prism medium is greater for violet than for red light, so violet light refracts more.

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14
Q

Does frequency of light change

A

Frequency of light does not change.

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15
Q

What is the relationship between wavelength, speed of light and angle in refraction

A

The wavelength and speed of light changes with the same ratio as the angles when light is refracted by a medium.

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16
Q

What is the critical angle

A

The critical angle is the angle of incidence in a medium when the angle of refraction in air is 90 degrees.

This is only relevant when light travels from a higher refractive index medium to a lower refractive index medium.

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17
Q

What happens if the angle of refraction is increased past 90 degrees

A

No light is refracted and total internal reflection takes place.

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18
Q

When angle in the material is less than the critical angle what happens

A

Most light is refracted, there is a weak partially reflected ray.

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19
Q

When angle in the material is equal to the critcal angle what happens

A

Light is refracted at 90 degrees, there is a stronger reflected ray.

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20
Q

When angle in the material is bigger than the critical angle what happens

A

No light refracts. All light is reflected. Total internal reflection occurs.

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21
Q

What is the formula for critical angle

A

Sin0c = 1/n

where n is refractive index.

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22
Q

What 3 things can all waves do

A

reflect, refract, diffract.

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23
Q

What is the relationship between diffraction and wavelength

A

Longer wavelengths diffract more than shorter wavelengths.

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24
Q

What is interference?

A

When two waves meet they combine to produce a new pattern - this is called interference.

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25
Q

What is interference evidence for

A

Interference is evidence for the wave model of light.

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26
Q

What two ways can waves interfere in

A

Constructive interference and destructive interference.

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27
Q

What 3 things does pattern of interference depend on

A

The pattern depends on the wave direction, amplitude and wavelength.

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28
Q

What must be true to observe interference patterns

A

To observe interference patterns the waves must come from coherent sources.

29
Q

What makes waves coherent

A

Coherent waves must have a constant phase relationship (but are not necessarily in phase)

30
Q

When does constructive interference occur

A

Constructive interference occurs when waves meet in phase (crest meets crest/trough meets trough)

31
Q

What does constructive interference cause

A

Constructive interference results in an increase in amplitude.

32
Q

When does destructive interference occur

A

Destructive interference occurs when waves meet out of phase (creast meets trough)

33
Q

What does destructive interference cause

A

Destructive interference results in a reduced (or zero) amplitude.

34
Q

When do interference patterns occur

A

when two coherent sources meet.

35
Q

How can two coherent sources be made

A

by making two sets of waves from a single coherent monochromatic (single frequency) light source directed towards a double slit.

36
Q

When does a maximum (or “bright fringe”) occur

A

when the waves meet in phase and constructive interference has taken place.

37
Q

When does a minimum (or “dark fringe”) occur

A

when the waves meet out of phase and destructive interference has taken place.

38
Q

What must happen for a maximum to be made

A

one wave must have travelled whole number of wavelengths further than the other.

39
Q

What is the formula for path difference of a maximum

A

path difference for a maximum = mλ

where m is the order number of the maxima and λ is wavelength.

40
Q

What is the path difference at the central maximum

A

at the central maximum (zero order) both waves have travelled the same distance so the path difference is 0

41
Q

What must happen for a minimum to be made

A

For a minimum to be made, one wave must have travelled an odd number of half wavelengths further than the other.

42
Q

What is the formula for path difference for a minimum

A

path difference for a minimum = (m+1/2)λ

NOTE: first minimum occurs when the path difference is λ/2 so m = 0 at first minima

43
Q

What factors effect fringe seperation

A

Fringe seperation can be increased by:
increasing wavelength
Decreasing slit seperation
Increasing the distance between the slits and the screen.

44
Q

Whaat does a diffraction grating do

A

A diffraction grating makes an interference pattern brighter and more spaced out. It lets a lot more light through than a double slit. It contains many equally spaced lines very close together.

45
Q

What is the diffraction grating equation

A

dsin0 = mλ

where:
d = the line of seperation of the grating (metres)
0 = angle from the zero order to the mth order (degrees)
λ = wavelength (metres)
m = order of the maximum

46
Q

How do you find the spacing between lines in a grating (in metres)

A

d = 1mm/number of lines

(Milimeters on top unless stated otherwise)

47
Q

How can you increase the angle of diffraction (and therefore the distance between fringes)

A

Increase wavelength of the lightsources
Decrease the slit seperation (d) (more lines per mm)

moving the screen further away causes increase in fringe seperation but not angle.

48
Q

Why is the central maximum white

A

All colours constructively interfere.

49
Q

What is the approximate wavelength of red light

A

650nm

50
Q

What is the approximate wavelength of green light

A

540nm

51
Q

What is the approximate wavelength of blue light

A

490nm

52
Q

Highest order maxima are …

A

Spectra (have coloured edges)

53
Q

What is true about the angle at which maxima occur

A

It is bigger for longer wavelengths, therefore the maxima for red light appear at larger angles than the maxima for blue light.

54
Q

What are the 3 key features of the white light interference pattern (using a grating)

A

The central fringe is white as for all colours of light the path difference is 0 (pd = (0*λ))

Violet light has a shorter wavelength than red light so violet light pattern is less spread out than for red light.

Many spectra are produced, symmetrical about the central maximum.

55
Q

What happens when white light is shone through a prism

A

The light is split into the visible spectrum

56
Q

What are the 4 key features of the white light refraction pattern

A

Only one spectrum produced by refraction.

Violet deviated the most, red the least as violet has a higher refractive index for mediums compared to red light.

Bright image compared to a grating spectrum that is less intense as energy is divided between several spectra.

Less spread out than a grating spectrum.

57
Q

Describe the bohr model of the atom

A

It states that the orbits of electrons are quantised. This means that they can only exist at certain distances from the nucleus. Electrons exist only in discrete energy levels.

58
Q

Is the energy between each level the same

A

The energy between each energy level is not the same.

59
Q

What is the lowest energy level called

A

The ground state

60
Q

What does the term excited state mean

A

If an electron has been moved from its normal level to a higher energy it is said to be in an excited state.

61
Q

How can you move an electron from the ground state

A

It is possible to move an electron from the ground state to an excited state by inputting energy. This is often done in the form of light.

62
Q

What causes emmision lines on a spectrum

A

Each emmision line on a spectrum occurs when an electron makes a transition between an excited state, E2, an a lower state, E1.

63
Q

What happens to excess energy when an electorn moves from an excited state to a lower stated

A

The excess energy is emmited as a photon of light. The frequency of the radiation emmited depends on the energy of the photon. The energy of the photon depends on the nergy levels the electron jumps between.

64
Q

What is the formula for energy of photons.

A

hf = E2-E1

where:
h = plancks constant (6.63*10^-34Js)
f = frequency (Hz)
E2 and E1 = energy levels in an atom (J)

65
Q

What are the 3 types of spectra

A

Continnous spectrum
Line emmision spectra
Line absorption spectra

66
Q

What produces a continuous spectrum

A

Produced by an object or gases which radiate heat.

67
Q

What produces a line emmision spectra

A

Produced by electrons making transition from excited states to a lower energy level releasing a photon of a particular frequency.

68
Q

What produces a line absorption spectra

A

Produced when photons of light pass through a gas. The photons with the same energy as the energy gaps in the atoms can be absorbed.

69
Q

Define light irradiance on a surface

A

Light irradiance on a surface is defined as the power on every metre squared.

70
Q

State the irradiance formula

A

I = P/A

where:
I = Irradiance (Wm^-2)
P = power (W)
A = area (m^2)

71
Q

What is the relationship between light irradiance and distance from a point source

A

Light irradiance is inversely proportional to the square of the distance from a point source, or:

I1d1^2 = I2d2^2

Where:
I1 = irradiance at point 1 (Wm^-2)
I2 = irradiance at point 2 (Wm^-2)
d1 = distance to point 1 (m)
d2= distance to point 2 (m)

Higher physics (4 decks)

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