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IGCSE Physics - Waves > Light > Flashcards

Light Flashcards

1
Q

What types of waves can be reflected or refracted?

A

All waves, whether longitudinal or transverse

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2
Q

When does reflection occur?

A

Reflection occurs when:
A wave hits a boundary between two media and does not pass through, but instead stays in the original medium.

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3
Q

When does refraction occur?

A

Refraction occurs when:
A wave passes a boundary between two different transparent media and undergoes a change in direction of waves at a boundary.

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4
Q

Where are angles measures on a ray diagram for reflection or refraction?

A

Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary.

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5
Q

What is the angle of the wave approaching the boundary called?

A

The angle of the wave approaching the boundary is called the angle of incidence (i)

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6
Q

What is the angle of the wave leaving the boundary called? (in reflection)

A

The angle of the wave leaving the boundary is called the angle of reflection (r).

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7
Q

What is the law of reflection?

A

Angle of incidence (i) = Angle of reflection (r)

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8
Q

What is used to show the direction the wave is travelling?

A

When drawing a ray diagram an arrow is used to show the direction the wave is travelling.

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9
Q

What is the arrow on a ray used for on a ray diagram?

A

When drawing a ray diagram an arrow is used to show the direction the wave is travelling.

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10
Q

Describe the incident ray

A

An incident ray is the ray approaching the boundary and has an arrow pointing towards the boundary

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11
Q

Describe a reflected ray

A

An reflected ray is the ray leaving the boundary and has an arrow pointing away from the boundary

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12
Q

What is the angle of incidence labelled as?

A

The angles of incidence is usually labelled i

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13
Q

What is the angle of reflection usually labelled as?

A

The angles of reflection is usually labelled r

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14
Q

Where are the angles of incidence and reflection measured from?

A

The angles are measured from the normal

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15
Q

What happens when the ray of light hits the boundary between two different medias on refraction ray diagrams?

A

At the boundary, the rays of light undergo a change in direction.

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16
Q

When the rays of light on refraction ray diagram change directions due to light passing through different, what does the direction depend on?

A

The direction is taken as the angle from a hypothetical line called the normal.

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17
Q

Describe the normal

A

It is a perpendicular line to the surface of the boundaries and is usually represented by a straight dashed or dotted line

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18
Q

What does the change in direction of the ray in refraction depend on?

A

The change in direction depends on the difference in density between the two media; From less dense to more dense (e.g air to glass), light bends towards the normal
From more dense to less dense (e.g. glass to air), light bends away from the normal
However, When passing along the normal (perpendicular) the light does not bend at all

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19
Q

What happens when the light travels from a less dense medium to more dense medium?

A

From less dense to more dense (e.g air to glass), the rays will slow down and light bends towards the normal and so r < I.

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20
Q

What happens when the light travels from a more dense medium to less dense medium?

A

From more dense to less dense (e.g. glass to air), the rays will speed up and light bends away from the normal and so r > i .

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21
Q

When happens to the light
passing along the normal in refraction (perpendicular)?

A

When passing along the normal (perpendicular) the light does not bend at all.

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22
Q

What are the only properties that change during refraction, and what does not change?

A

The only properties that change during refraction are speed and wavelength – the frequency of waves does not change.

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23
Q

What do different frequencies account for and give an example?

A

Different frequencies account for different colours of light (red has a low frequency, whilst blue has a high frequency)

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24
Q

What happens to colours when light refracted?

A

When light refracts, it does not change colour (think of a pencil in a glass of water), therefore, the frequency does not change.

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25
Q

What is a virtual image and how can it be represented on a diagram?

A

A virtual image is an image that cannot be formed on a screen and can be represented as the rays do not meet at the image.

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26
Q

Explain what happens to the wavelength of light when it passes from air into water. (Not light ray)

A

The wavelength decreases;
because wave speed decreases and frequency remains constant.

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27
Q

What is refraction?

A

A change in direction of waves at a boundary.

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28
Q

If light light speeds up on entering a new medium, what does this inform us about the new medium it enters.

A

If light speeds up on entering a new medium, then the medium is “less optically dense”

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29
Q

If light slows up on entering a new medium, what does this inform us about the new medium it enters?

A

If light slows down as it enters a new medium, the new medium is “more optically dense”.

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30
Q

What happens to light entering a material with higher optical density?

A

It slows down and turns towards the normal.

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31
Q

What happens to the wavelength of waves when they are reflected?

A

It does not change

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32
Q

What is white light?

A

White light is combination of all colours

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33
Q

What is black light?

A

Black light is the absence of light

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34
Q

What is the aim of the practical for investigating refraction?

A

To investigate the refraction of light using rectangular blocks, semi-circular blocks and triangular prisms.

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35
Q

What is the independent variable for the practical investigating refraction?

A

Shape of the block

36
Q

What is the dependent variable for the practical investigating refraction?

A

Direction of refraction

37
Q

What are the control variables for the practical investigating refraction?

A

Control variables:
Width of the light beam
Same frequency / wavelength of the light

38
Q

What are the equipment in the experiment for the practical investigating refraction?

A

Ray box, protractor, sheet of paper, pencil, ruler, Perspex blocks (rectangular block, semi-circular block & prism)

39
Q

What is the purpose of the ray box for the practical investigating refraction?

A

To provide a narrow beam of light to reflect in the mirror.

40
Q

What is the purpose of the protractor for the practical investigating refraction?

A

To measure the light beam angles.

41
Q

What is the purpose of the sheet of paper in the practical investigating refraction?

A

To mark with lines for angle measurement.

42
Q

What is the purpose of a pencil in the practical investigating refraction?

A

To mark perpendicular line and angle line on paper.

43
Q

What is the purpose of the ruler in the practical investigating refraction?

A

To draw lines on paper.

44
Q

What is the purpose of the Perspex blocks in the practical investigating refraction?

A

To refract the light beam.

45
Q

Describe the method to carry out an experiment to investigate refraction.

A
  1. Place the glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
  2. Switch on the ray box and direct a beam of light at the side face of the block
  3. Mark on the paper:
    - A point on the ray close to the ray box
    - The point where the ray enters the block
    The point where the ray exits the block
    - A point on the exit light ray which is a distance of about 5 cm away from the block
  4. Draw a dashed line normal (at right angles) to the outline of the block where the points are
  5. Remove the block and join the points marked with three straight lines
  6. Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
  7. Repeat the procedure for each shape of perspex block (prism and semi-circular)
46
Q

Describe what happens when the light rays enter the Perspex block.

A

For light rays entering the perspex block, the light ray refracts towards the central line and so i > r (angle of incidence is greater than angle of reflection).

47
Q

Describe what happens when the light rays exit the Perspex block.

A

For light rays exiting the perspex block, the light ray refracts away from the central line and so i < r (angle of refractions is greater than angle of incidence).

48
Q

Systematic Error in the practical investigating refraction & Snell’s Law and what is the solution.

A

An error could occur if the 90° lines are drawn incorrectly

Solution: use a set square to draw perpendicular lines

49
Q

Random Errors in the practical investigating refraction & Snell’s Law and what are the solutions.

A

The points for the incoming and reflected beam may be inaccurately marked
Solution: use a sharpened pencil and mark in the middle of the beam
The protractor resolution may make it difficult to read the angles accurately
Solution: Use a protractor with a higher resolution

50
Q

Safety considerations in the practical investigating refraction & Snell’s Law and how to protect ourselves?

A

The ray box light could cause burns if touched
Solution: Run burns under cold running water for at least five minute
Looking directly into the light may damage the eyes
Solution: Avoid looking directly at the light
Solution: Stand behind the ray box during the experiment
Keep all liquids away from the electrical equipment and paper

51
Q

What is Snell’s Law?

A

n = sin i/sin r

52
Q

What is n in the Snell’s Law equation?

A

n = the refractive index of the material

53
Q

What is i in the Snell’s Law equation?

A

i = angle of incidence of the light (°)

54
Q

What is r in the Snell’s Law equation?

A

r = angle of refraction of the light (°)

55
Q

What is sin in the Snell’s Law equation?

A

‘Sin’ is the trigonometric function ‘sine’ which is on a scientific calculator.

56
Q

What is the number range for the refractive index of a material?

A

Greater than one, but less than 4

57
Q

If an object is more optically dense, what does that inform us regarding its refractive index?

A

Objects which are more optically dense have a higher refractive index.

58
Q

If an object is less optically dense, what does that inform us regarding its refractive index?

A

Objects which are less optically dense have a lower refractive index.

59
Q

What is the aim of the practical: investigating Snell’s Law?

A

To investigate the refractive index of glass, using a glass block.

60
Q

What is the independent variable in the practical: Investigating Snell’s Law?

A

Angle of incidence, i

61
Q

What is the dependent variable in the practical: Investigating Snell’s Law?

A

Angle of refraction, r

62
Q

What is the control variables in the practical: Investigating Snell’s Law?

A

Use of the same perspex block
Width of the light beam
Same frequency / wavelength of the light

63
Q

What are equipment utilised in the practical: investigating Snell’s Law?

A

Ray box, protractor, sheet of paper, pencil, ruler and Perspex rectangular block.

64
Q

What is the purpose of the ray box in the practical: Investigating Snell’s Law?

A

To provide a narrow beam of light to reflect in the mirror.

65
Q

What is the purpose of the protractor in the practical: Investigating Snell’s Law?

A

To measure the Light beam angles.

66
Q

What is the purpose of the sheet of paper in the practical: Investigating Snell’s Law?

A

To mark with lines for angle measurement.

67
Q

What is the purpose of a pencil in the practical: Investigating Snell’s Law?

A

To mark perpendicular Line and angle Lines on paper.

68
Q

What is the purpose of the ruler in the practical: Investigating Snell’s Law?

A

To draw lines on paper

69
Q

What is the purpose of the Perspex rectangular block in the practical: Investigating Snell’s Law?

A

To refract the light beam.

70
Q

Describe a method to investigate Snell’s Law

A

I. Place the glass block on a sheet of paper, and carefully draw around the block using a pencil
2. Draw a dashed line normal (at right angles) to the outline of the block
3. Use a protractor to measure the angles of incidence to be studied and mark these lines on the paper
4. Switch on the ray box and direct a beam of light at the side face of the block at the first angle to be investigated
5. Mark on the paper:
• A point on the ray close to the ray box
• The point where the ray enters the block
• The point where the ray exits the block
• Apoint on the exit light ray which is a distance of about 5 cm
away from the block
6. Remove the block and join the points marked with three straight lines
7. Replace the block within its outline and repeat the above process for a rays striking the block at the next angle
8. Record your results on a table of results

71
Q

What can happen sometimes when light is moving from a denser medium towards a less dense one and does not get refracted?

A

When this happen, the all light is reflected. This is known as total internal reflection.

72
Q

When does total internal reflection occur?

A

It occurs when the angle of incidence is greater than the critical angle and the incident material is denser than the second material.

73
Q

What the two conditions for total internal reflection?

A

The angle of incidence is greater than the critical angle and the incident material is denser than the second material.

74
Q

What can total internal reflection be utilised in?

A

Total internal reflection is utilised in:
Optical fibres eg. endoscopes or communication
Prisms eg. periscopes

75
Q

What happens when the angle of refraction is exactly 90°?

A

When the angle of refraction is exactly 90°, the light is refracted along the boundary.

76
Q

Give examples of when total internal reflection is used to reflect light along optical fibres.

A

Communications
Endoscopes
Decorative lamps
Safety reflectors on bicycles, cars and roads
In medicine; to see within the human body

77
Q

How is light travelling down an optical fibre totally internally reflected?

A

Light travelling down an optical fibre is totally internally reflected each time it hits the edge of the fibre.

78
Q

How are optical fibers used in medicine?

A

Endoscopes use optical fibres to produce an image of inside the body. A doctor can insert a bundle of optical fibres into the body. This allows the doctor to see an image of the inside of the body clearly, and help them diagnose diseases.

79
Q

Give examples of how can prisms be used in optical instruments.

A

Prisms are used in a variety of optical instruments, including:
Periscopes
Binoculars
Telescopes
Cameras

80
Q

What is a periscope?

A

A periscope is a device that can be used to see over tall objects and consists of two right-angled prisms

81
Q

How can a periscope be used to see over tall objects?

A

Periscopes consist of two right-angled prisms and light is totally internally reflected in both these prisms.

82
Q

What happens the angle of incidence is increased?

A

As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90° and when the angle of refraction is exactly 90° the light is refracted along the boundary

83
Q

What is the equation to calculate critical angle?

A

sin c = 1/n

84
Q

What is the equation for calculating the refractive index using the critical angle?

A

n = 1/sin c

85
Q

How are the refractive index and critical angle related?

A

The larger the refractive index of a material, the smaller the critical angle.

86
Q

Light rays inside a material with a high refractive index are more likely to be…

A

Light rays inside a material with a high refractive index are more likely to be totally internally reflected

IGCSE Physics - Waves (4 decks)

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