Refraction

Question 1

Refraction

Answer 1

Where a wave changes direction as it enters a different medium as a result of it changing speed

Question 2

Why does light refract

Answer 2

Different materials have different optical density

Question 3

How is optical density measured?

Answer 3

By the refractive index

Question 4

When light enters a more optically dense material…

Answer 4

…it refracts towards the normal

Question 5

When light enters a less optically dense material…

Answer 5

…it refracts away from the normal

Question 6

When a light hits a surface normally…

Answer 6

…there is no refraction

Question 7

Conditions for total internal refraction to occur

Answer 7

• Light moving towards a material with a lower refractive index
• The light hits the boundary at / above the critical angle

Question 8

Critical angle

Answer 8

The angle of incidence that results in an angle of refraction of 90° (when traveling into a less optically dense material)

Question 9

What is the function of optical fibres?

Answer 9

Transmiting light over long distances

Question 10

Structure of a fibre optic cable

Answer 10

Core - Cladding - Protective layer

Question 11

Advantages of using optical fibres (over copper cables)

Answer 11

• Less energy loss per meter (longer distances between signal being boosted)
• High frequency of light allows more data transfer per seccond
• No electrical interference (fibres can be bundled together)
• More secure (cannot be detected/tapped into)
• Lighter + smaller volume

Question 12

Role of the cladding

Answer 12

• Protects the core from scratches/moisture
• Increases the critical angle - only rays with large angles to the normal are transmitted (reduces multimode dispersion)

Question 13

Multimode / multipath dispersion

Answer 13

When light travels down an optical fibre in different paths, rays reach the end at different times and broaden the pulse of light

Question 14

Problems with multipath dispersion

Answer 14

Pulses of light merge into each other and change the information being transferred

Question 15

Solutions to multimode dispersion

Answer 15

• Leave bigger gaps between pulses
• Use cladding (and make the initial signal brighter to make up for greater loss of signal)

Question 16

Material dispersion

Answer 16

• Light of different wavelengths travel at different speeds in glass
• Rays will reach the detector at different times

Question 17

Solutions to material dispertion

Answer 17

Use monochromatic light

Question 18

Absorption in optical fibres

Answer 18

Impurities in the glass absorb light

Question 19

Solutions to absorpsion

Answer 19

• Boost signal at regular intervals
• Use infrared light to minimise absorption