Light and the Electromagnetic Spectrum

Question 1

What is the relationship between the incident angle and the reflection angle?

Answer 1

incident angle = reflection angle

Question 2

Explain specular reflection on smooth surfaces

Answer 2

On a smooth surfaces, all light incident rays exist at the same angle.

Question 3

Describe diffuse reflection

Answer 3

For diffusion reflection, this is where light hits a rough surface and the incident ray is reflected at many angles.

Question 4

How does light behave when entering a denser material during refraction?

Answer 4

Light bends towards the normal line.

Question 5

How does light behave when entering a less denser material during refraction?

Answer 5

Light bends away from the normal line.

Question 6

Explain the concept of Total Internal Reflection (TIR)

Answer 6

TIR occurs when light travels from a denser medium to a less dense one and the angle of incidence exceeds the critical angle, causing the light to reflect back into the denser medium instead of refracting out.

Question 7

What is different between each colour in visible light?

Answer 7

Each colour has a specific wavelength.

Question 8

How does white light form?

Answer 8

White light is composed if all colours together.

Question 9

Why do objects appear to have a specific colour?

Answer 9

Objects appear to gave a certain colour because they reflect only that specific colour of light, absorbing all other colours.

Question 10

Define focal length

Answer 10

The distance between the lens and the focal point.

Question 11

What is the focal point?

Answer 11

The focal point is where all horizontal rays converge after passing through the lens.

Question 12

Explain the relationship between focal length and lens power.

Answer 12

Power of lens is inversely proportional to the focal length; Thicker lens means shorter focal length, so greater power.

Question 13

What are concave lenses? (3)

Answer 13

1. Caves inwards
2. Thinner at centre than the edges
3. Spreads light outwards and further – used for short sightedness. This is because light is focused in front of the retina, so needs to be spread out slightly to be able to be focused onto retina.

Question 14

What are convex lenses? (4)

Answer 14

1. Thicker at centre
2. Focuses light inwards
3. Horizontal rays focus onto focal point
4. Used for magnifying glasses, binoculars and to correct long-sightedness as it focuses the rays closer.

Question 15

Describe electromagnetic waves

Answer 15

They are transverse waves, all travel at the same speed in a vacuum (3 x 10 to the power of 8m/s) and in space all waves have the same velocity of speed of light.
EM waves do not need particles to move.

Question 16

What are the EM waves?

Answer 16

radio waves, microwaves, infra-red, visible light, ultraviolet, x-ray, gamma
radio waves - highest wavelength

Question 17

How do materials interact with electromagnetic waves?

Answer 17

Materials interact with EM waves differently depending on the wavelength; for example glass can transmit visible light, reflect/absorb UV and IR.

Question 18

Explain how bodies emit radiation

Answer 18

All bodies emit radiation: the higher the temperature the more intense and more wavelengths will be emitted. Temperature of the earth is also maintained this way; amount of energy received and emitted from the sun.
It must radiate the same average power than it absorbs to remain at a constant temperature.

Question 19

What happens if a body absorbs more power than it emits?

Answer 19

If it absorbs more power than it emits – the temperature will increase

Question 20

Describe the role of short wavelength infrared radiation from the sun in maintaining the Earth’s temperature

Answer 20

Short wavelength infra-red radiation from the sun reaches the earth, some is reflected by the atmosphere, most reaches the atmosphere. The energy is absorbed and reemitted as longer length IR radiation. This is mostly absorbed by the atmosphere and keeps Earth warm.

Question 21

What are the dangers with high EM waves?

Answer 21

Higher frequency EM waves have more energy, so exposure can transfer too much energy to cells, causing them to mutate and potentially damage them (causing cancer).

Question 22

What are the dangers with microwaves?

Answer 22

internal heating of body cells

Question 23

What are the dangers with infra-red waves?

Answer 23

skin burns

Question 24

What are the dangers with UV waves?

Answer 24

damage to surface cells and eyes, leading to skin cancer

Question 25

What are the dangers with x-ray or gamma rays?

Answer 25

mutation or damage to cells in the body

Question 26

What are the uses of radiowaves?

Answer 26

Communications, satellite transmissions (they can be produced by oscillations in electrical circuits or they can induce oscillations in electrical circuits).

Question 27

What are the uses of microwaves?

Answer 27

cooking, communication

Question 28

What are the uses of infra-red waves?

Answer 28

cooking, thermal imaging, short range communications, optical fibres

Question 29

What are the uses of visible light?

Answer 29

vision, photography, illumination

Question 30

What are the uses of x-rays?

Answer 30

observing structures of objects, airport/medical scanners

Question 31

What are the uses of gamma rays?

Answer 31

sterilising food/medical equipment, treating cancer

Question 32

What can changes in atoms and nuclei do?

Answer 32

It can generate radiations over a wide frequency range and be caused by absorption of a range of radiation.

Question 33

CORE PRACTICAL - Investigate refraction in rectangular glass blocks in terms of the interaction of electromagnetic waves with matter (7)

Answer 33

1. Set up equipment in a darkened room. Place the glass block on a paper, outlining its position for consistency throughout this experiment.
2. Draw a normal line (90 degrees to the glass surface) using a protractor.
3. Draw three lines a guides for the angles of incidence (you will shine light onto these lines into the block). Example angles are 20, 40 and 60.
4. Shine light along each line using a the ray box with a single slit to create a narrow beam, marking where it exits the block.
5. Use a protractor to measure angles of refraction.
6. Compare angles for glass into air (refraction smaller) and air into glass (refraction greater).
7. Plot results on a graph: angle of refraction against angle of incidence with one line showing glass into air and another showing air into glass.

Question 34

CORE PRACTICAL - Investigate how the nature of a surface affects the amount of thermal energy radiated or absorbed (6)

Answer 34

1. Place 4 beakers and surround them each with a different material. (Black material, any other coloured material, white and silver). Place a thermometer in each of the beakers.
2. Boil the kettle and pour water in each of the beakers, ensuring they all have the same volume, and cover each beaker with a lid, to minimise heat loss.
3. Record the initial temperature of each beaker and start the stopwatch.
4. Record the temperature of each beaker at regular time intervals (every two minutes for a total of 20 minutes).
5. Plot a graph of temperature against time, drawing a different line for each beaker. The gradient will show the rate of cooling for each of the beakers.
6. Results should show that the matte black beaker cools the fastest and the silver beaker cools the slowest.