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A-level AQA Physics > 08 Electromagnetic Radiation > Flashcards

08 Electromagnetic Radiation Flashcards

1
Q

What are the different types of radiation?

A

-radio waves
-microwaves
-infrared radiation
-visible light
-ultra violet
-x-rays
-gamma rays

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2
Q

What does visible light form part of?

A

The electromagnetic spectrum.

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3
Q

What is the only part of the electromagnetic spectrum that our eyes can detect?

A

Visible light

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4
Q

What are the similarities between the different parts of the electromagnetic spectrum?

A

-all travel at the speed of light in a vacuum
-all transverse waves
-all massless
-all can propagate through a vacuum

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5
Q

What is the law of reflection?

A

Angle of incidence = angle of reflection

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6
Q

What are the angles of incidence and reflection measured between?

A

The ray and the normal

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7
Q

When light travels from air into glass, where is the light refracted?

A

Towards the normal

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8
Q

When light travels from glass into the air, where is the light refracted?

A

Away from the normal

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9
Q

What happens if the light incident is perpendicular to a glass block?

A

It continues in a straight line without refracting.

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10
Q

What is refraction?

A

Light incident upon a glass block at an angle changes direction.

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11
Q

What happens when a light incident upon a glass block at an angle.

A

It changes direction (refraction).

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12
Q

How does light leave a rectangular glass block?

A

Parallel to the ray entering.

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13
Q

How do you find the refractive index of a substance?

A

(Speed of light in a vacuum) / (speed of light in the substance)

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14
Q

What is the speed of light?

A

3x10⁸m s‐¹

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15
Q

What is the unit for refractive index?

A

Nothing

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16
Q

What is the value for refractive index always between?

A

1.00 and 4.05

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17
Q

When light passes from a low refractive index to a high refractive index, how does it refract?

A

Towards the normal

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18
Q

When light passes from a low refractive index to a high refractive index, what happens to its speed?

A

It decreases

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19
Q

When light passes from a low refractive index to a high refractive index, what happens to its wavelength?

A

It reduces

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20
Q

When light passes from a low refractive index to a high refractive index, what happens to its frequency?

A

It’s constant

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21
Q

When light passes from a high refractive index to a low refractive index, how does it refract?

A

Away from the normal

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22
Q

When light passes from a high refractive index to a low refractive index, what happens to its speed?

A

It increases

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23
Q

When light passes from a high refractive index to a low refractive index, what happens to its wavelength?

A

It increases

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24
Q

Who discovered the relationship between angle of incidence and angle of refraction?

A

Willieboard snellius

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25
Q

Snell’s law of refraction:

A
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26
Q

When light travels through air, what should you assume the refractive index of air to be and why?

A

1.00 because light in air almost travels as fast as light in a vacuum.

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27
Q

What is the uncertainty in the angle measurement equal to?

A

The precision of the protractor

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28
Q

What is the definition of a critical angle?

A

The critical angle is equal to the incidence angle within a substance which results in a refracted ray having an angle of refraction of 90°.

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29
Q

The actual critical angle for a red light is lower than a blue light.
Explain why TIR is more likely to happen when using a red light?

A

There are more angles between the lower critical angle and 90° than the higher critical angles.

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30
Q

If the incident angle is equal to the critical angle, what is the angle of refraction?

A

90°

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31
Q

During TIR what does the reflected angle look like?

A

Identical to the angle of incidence

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32
Q

When the incident angle exceeds the critical angle, what occurs?

A

Total internal reflection (TIR)

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33
Q

What must happen for total internal reflection to occur?

A
  1. The angle of incidence must me greater than the critical angle.
  2. The ray of light must be travelling from a high refractive index to a low refractive index.
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34
Q

How can you calculate refractive index using the critical angle formula?

A

Sin 90 = 1 so
Sin θc = n2/n1 or
Sin θc = 1/n1

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35
Q

What is an optical fibre?

A

A core of glass of a high refractive index surrounded by cladding made of glass of a lower refractive index.

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36
Q

How does light travel along the optical fibre?

A

By undergoing total internal reflection.

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37
Q

What is an optical fibre made up of?

A

Cladding (low refractive index) and a core (high refractive index).

38
Q

What is the purpose of a core in an optical fibre?

A

The light travels along the core undergoing total internal reflection at the boundary between the core and the cladding.

39
Q

What is the purpose of the cladding in an optical fibre?

A
  • the cladding prevents light from crossing over between two touching fibres
  • it prevents damage to the core (which could cause light to escape).
  • if the optical fibre is being used for communication the cladding keeps the information secure so preventing fraud.
    -increases the critical angle which reduces moral dispersion.
40
Q

What does this graph show?

A

How the refractive index of a step index optical fibre changes.

41
Q

Describe the refractive index of the core and the cladding using the graph.

A
  1. The core of the fibre has a constant refractive index.
  2. The cladding has a lower, but also constant, refractive index.
42
Q

Explain what is modal dispersion (multipath dispersion)?

A

The extra distance that some light beams take.

43
Q

What is pulse broadening?

A

Modal dispersion increasing the duration of a light pulse traveling along an optical fibre.

44
Q

What does modal dispersion and pulse broadening cause?

A

The pulses to overlap therefore smearing which distorts the information.

45
Q

How can modal dispersion be reduced?

A

By making the core of an optical fibre very thin.

46
Q

Why does material dispersion occur?

A

As not all frequencies are refracted by the same angle in the fibre.

47
Q

Why does chromatic dispersion occur?

A

As different frequencies travel at different speeds.

48
Q

Which travels faster? Blue light or red light?

A

Red light

49
Q

What can light travelling through a fibre be reflected by?

A

Impurities

50
Q

What are the advantages of a narrow core in a fibre optic?

A

•loses less light
•increases the probability of TIR
•light is less likely to fall below the critical angle.
•improves data transfer rate.

51
Q

Give 2 examples of uses of optical fibre?

A
  1. Cables made of optical fibres are used for Internet communications. This allows data to be transmitted at higher rates.
  2. An endoscope uses a bundle of optical fibre to produce images inside of the body. This enables a more accurate medical diagnosis.
52
Q

What are coherent sources of light?

A

They both have the same constant frequency and constant phase angle.

53
Q

What safety precautions should you use when working with lasers?

A

•don’t shine lasers into anyone’s eye
•wear laser safety glasses.

54
Q

What is monochromatic light?

A

Light of only one specific wavelength (frequency).

55
Q

What is fringe spacing (w)?

A

The distance from the centre of one bright fringe to the centre of the next .

56
Q

In youngs double slit experiment, what would be seen on the screen?

A

Fringes

57
Q

In the fringe spacing formula, what is ‘D’?

A

Distance to screen

58
Q

Wn the fringe spacing formula, what is ‘s’?

A

Slit spacing.

59
Q

What is the wavelength of red light?

A

700nm

60
Q

What is the wavelength of blue light?

A

400nm

61
Q

How will the fringe pattern change if the red light was replaced by a blue light in a double slit experiment?

A

•fringes will move closer together.
•central fringe doesn’t move
•fringes will now be blue.

62
Q

What is this graph? (Double slit)

A

Intensity graph for double slit experiment.

63
Q

What do you notice about the width of each fringe in an intensity graph for the double slit experiment?

A

They are equal in width.

64
Q

In the double slit experiment, why is the central fringe brighter than all the other fringes?

A

The further the light has to travel , the more it attenuates. The central fringe is when the path difference is 0 so it has to travel the least.

65
Q

In the double slit experiment, explain why in reality the minimas of an intensity graph does not reach the x-axis?

A

One ray of light has to travel further, which means it attenuates more, they don’t cancel eachother out perfectly so the destructive interference isn’t perfect.

66
Q

What does attenuate mean?

A

To make something less or weaker.

67
Q

What property of laser light makes the double slit experiment possible?

A

Coherent

68
Q

Is a white light from an LED a coherent beam?

A

No.

69
Q

When using a white LED in the double slit experiment, what must you do to create a single point source?

A

Position a single slit after the lamp.

70
Q

When using a white LED in the double slit experiment, why must the single slit be narrow?

A

•it allows the wavefront to hit the double slit sources so that they emit light in phase (coherent).
•it produces a wide diffracted beam which lights up both slits.

71
Q

Describe the appearance of interference fringes produced by a white light source?

A
  • the central bright fringe is white
  • the side fringes are continuous spectra
  • the side of a fringe nearest the centre is blue/violet
    -the side of a fringe furthest from the centre is red.
72
Q

What is the beam going straight through the grating?

A

The zero order.

73
Q

How is the zero order labelled?

A

n = 0

74
Q

At the zero order (n=0) what is the path difference?

A

0λ

75
Q

On either side of the central maxima, what is there?

A

The first order diffracted maxima (n=1), then the second order (n=2), etc.

76
Q

What type of number are the visible maxima always?

A

Odd

77
Q

If there are 7 maxima visible on the screen, how many visible orders are there? Why?

A
  1. N=0 doesn’t count as a visible order and up to n=3 is visible.
78
Q

What is a diffraction grating?

A

A piece of optical equipment that creates a diffraction pattern when it diffracts.

79
Q

When shining light through a grating, for the rays of light shown to produce a constructive interference beam, what must the path difference be?

A

It must be equal to an integer number of wavelengths. eg. 0λ, 1λ, 2λ … nλ.
The beams of light must be coherent.

80
Q

What is total internal reflection? (TIR)

A

When the incident angle exceeds the critical angle.

81
Q

What does each element produce with coloured lines at specific wavelengths?

A

Emmission spectrum

82
Q

Explain an emission spectrum?

A

An element emits certain specific colours. The grating spreads these colours out depending on their wavelength. Hence the line spectra appear as a series of coloured lines at specific wavelengths.

83
Q

Explain absorption spectrum?

A

Shine a white light through a container of the element. The exact same wavelengths shown on the emission spectrum are now absorbed producing dark lines on a continuous spectrum background.

84
Q

What is like an elements finger print?

A

A line spectrum.

85
Q

When high density, hot matter goes through a diffraction grating what does it create?

A

A continuous spectrum.

86
Q

When hot gas goes through a diffraction grating, what does it create?

A

An emission spectrum

87
Q

When cold gas goes through a diffraction grating, what does it create?

A

Absorbtion spectrum

88
Q

Why can a diffraction grating split light into the colours that it is made up of?

A

Because light of different wavelengths are diffracted by different angles.

89
Q

What does the spectra of stars appear as?

A

An absorption spectra

90
Q

Why does a spectra of stars appear as an absorption spectra?

A

Because specific colours are absorbed by atoms in the outer atmosphere.

91
Q

How can someone determine a stars chemical composition?

A

By comparing the stars spectrum with the spectra of elements.

92
Q

Which of these elements are in the star?

A

•Helium
•Hydrogen

A-level AQA Physics (9 decks)

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