Waves, Light and Lasers

Question 1

In refraction why does the wave change direction

Answer 1

It is changing speed, it enters substance of different density

Question 2

Diffraction is when..

Answer 2

A wave spreads out, it has passed an opening about the size of the wave’s wavelength
It can also happen if a wave passes an obstacle

Question 3

Short or long wavelength on high frequency waves

Answer 3

Short

Question 4

When electromagnetic waves are used for communication, the size of the reciever has to be similar size as what?

Answer 4

The wavelength

Question 5

What are optical fibres

How does light travel down them and what does this depend on

Explain multiplexing

Answer 5

Long,flexible transparent glass or plastic fibres
Light travels by reflecting off the sides (TOTAL INTERNAL REFLECTION) this depends on the CRITICAL ANGLE of the substance
You can use multiplexing, sending many different messages along fibre at same time

Question 6

Total internal reflection can only happen inside..

Answer 6

A material that is more optically dense than the material surrounding it

Question 7

What are lasers and what can they be used for

Answer 7

They are narrow beams of light with single wavelength
Monochromatic and coherent
The light beams are in phase and do not diverge with same frequency
Can be used for guiding weapons and cutting materials

Question 8

What is the relation between energy and waves out of phase

What must the wave be like in order to be in phase

Answer 8

Waves out of phase transmit less overall energy

Wave must be monochromatic snd coherent

Question 9

How do Compact Discs work

Answer 9

Pits are on underside of CD where digital information is stored
CD player spins it and laser light is reflected from pits

The reflected pulses are detected as a digital signal (on and offs)and turned to electrical signals then transmitted to an amplifier

Question 10

What happens when ray of light hits a shiny surface

Answer 10

It is reflected. The angle of incidence is equal to the angle of reflection

Question 11

What happens if light enters (denser) substance equal to or smaller than critical angle

Answer 11

Light escapes and will be refracted

Question 11

What happens if light enters (denser) substance at angle larger than critical angle

Answer 11

Total internal reflection

Question 12

Each type of electromagnetic radiation is a transverse wave that:

Answer 12

Travels in straight lines

Has same speed through a vaccum

Question 13

What are radio waves used for in communication

Answer 13

Tv and radio stations

Question 14

What are microwaves used for in communication

Answer 14

To communicate using satellites

Question 15

What are infrared and light waves used for in communication

Answer 15

Communicating using optical fibres

Question 16

Advantage/disadvantage of using light for communication

Answer 16

Fast with small signal loss but sometimes requires optical fibres

Question 16

Advantage/disadvantage of using radio waves for communication

Answer 16

Can travel further via satellites of necessary but signal can be lost or weakened in the atmosphere

Question 17

Advantage/disadvantage of using electrical signals for communication

Answer 17

Reliable and can be boosted if weak but require wires

Signal can be lost through resistance

Question 18

How are wave based sensors such as telescopes and optical microscopes affected by diffraction

Answer 18

Diffraction limits the smallest thing they can detect

Two stars close together will be seen as a single star, diffraction makes light from the two stars spread and overlap

Question 19

Describe what each type of electromagnetic radiation has in common

Answer 19

All transverse waves, travel in straight line

Same speed through space (vaccum)

Question 20

Describe how types of electromagnetic radiation are different

Answer 20

Different wavelength and frequency

Question 21

Electromagnetic waves (including light) are faster than other ways of communication

Describe an early communication system

Answer 21

Morse code- digital communication
Series of on-off signals
Each letter of alphabet as dots and dashes