Deck 5: Signalling 1

Question 1

What is transverse

waves?

Answer 1

A transverse wave is a wave where the vibration is at right angles to the wave’s direction of travel.
- All electromagnetic waves are transverse

Question 2

Give an example of a longitudinal wave.

Answer 2

Sound.

Question 3

What is electromagnetic radiation?

Answer 3

Electromagnetic radiation is made up of two transverse waves. ( The things vibrating are electric and magnetic fields.)

Question 4

What effect does polarising have?

Answer 4

They only let vibrations of one direction in. This is called polarising the wave.

Question 5

What do you see if you shine light through two polarising filters at right angles to each other?

Answer 5

Then no light will get through as all directions of vibrations will be blocked.

Question 6

What type of waves can polarisation only happen on?

Answer 6

• Transverse waves.

- Not longitudinal waves.

Question 7

What happens to light when it reflects of a surface?

Answer 7

• Unpolarised light will reflect off the glass block and become partially polarised.

Question 8

Explain the use of polarisation in TV aerials?

Answer 8

1) TV aerials on people’s houses have the rods aligned horizontally. The reason for this is because TV signals are polarised by the orientation of the rods on the broadcasting aerial.
2) To receive a strong signal, you have to line up the rods on the receiving aerial with the rods on the transmitting aerial.

Question 9

Explain the use of polarisation in communication satellites.

Answer 9

They use different polarisations for signals in the same frequency band to help reduce the amount of interference between the signals.

Question 10

Explain how skiers use polaroid sunglasses?

Answer 10

• They block the glare of sunlight reflected off the snow.

Question 11

In an experiment, light is shone through a disc of a crystal called “Iceland spar”. The beam of light is less bright when it emerges from the crystal than when it enters. Next, a second identical disc of Iceland spar is placed in front of the first. The first disc is held steady while the second is rotated ( in the plane of the disc). The intensity of light emerging changes as the second disc rotates. At two points in each rotation, no light gets through at all.(5)

Answer 11

1) For ordinary light, the EM field vibrates in all planes at right angles to the direction of travel.
2) Iceland spar acts as a polariser.
3) When light is shone through the first disc, it only allows through vibrations in one particular plane, so emerges less bright.
4) As the two crystals are rotated relative to each other there comes a point when the allowed planes are at right angles to each other.
5) So all the light is blocked.