Light and lasers

Question 1

Morse Code

Answer 1

• The Morse code uses a series of dots and dashes to represent letters of the alphabet.
• This code is used by signalling lamps as a series of short and long flashes of light.
• It is an example of a digital signal.

Question 2

When a signal is sent by light, electricity, microwave, or radio…

Answer 2

It is almost instantaneous.

Question 3

Advantages and disadvantages of using light.

Answer 3

• Light signals can be easily sent with nothing more sophisticated than a torch.
• The signal needs to be coded and is not secure.
• Anyone can see what is being sent.
• Reqires line of sight.

Question 4

Advantages and disadvantages of using electricity,

Answer 4

• Relatively cheap and easy to use.
• Requires a wired connection between sender and receiver.
• Wires can be cut or damaged.
• Signals need to be reamplified at regular intervals because of energy loss as heat due to the electric current.

Question 5

Microwave Advantages and Disadvantages

Answer 5

• Can travel through clouds, fog and the various layers of the atmosphere without being completely lost.
• Multiple channels available
• Wide bandwidth
• Requires line of sight between receiver and transmitter.

Question 6

What are the advantages and disadvantages of using radio for communication?

Answer 6

• Diffracts around large objects.
• Can follow the curvature of the earth by reflection from ionosphere.
• Cannot carry as much information due to very long wavelengths compared to other EM radiations.

Question 7

Diffference between white light and laser light.

Answer 7

• White light is made up of different colours of different frequencies out of phase.
• Laser light has only a single frequency, is in phase and shows low divergence.

Question 8

Laser light is used to read from the surface of a compact disc (CD):

Answer 8

• The surface of the CD is pitted
• The pits represent the digital signal
• Laser light is shone onto the CD surface and the difference in the reflection provides the information for the digital signal.

Question 9

What happens when light travels from one material to another.

Answer 9

It is normally refracted,

Question 10

What happens when light passes from a more dense material into a less dense one?

Answer 10

The angle of refraction is larger than the angle of incidence.

Question 11

What is the angle of refraction called when it is 90°.

Answer 11

The critical angle.

Question 12

If the angle of incidence is bigger than the critical angle…

Answer 12

the light is reflected – this is total internal reflection.

Question 13

Optical Fibres

Answer 13

• Telephone conversations and computer data are transmitted long distances along optical fibres at the speed of light (200,000 km/s in glass).
• Some fibres are coated to improve reflection

Question 14

Endoscopy

Answer 14

• An endoscope allows doctors to see inside a body without the need for surgery.
• Light passes along one set of optical fibres to illuminate the inside of the body.
• The light is reflected.
• The reflected light passes up another set of fibres to an eyepiece or camera