Chapter 16 - Electromagnetic Waves

Question 0

What is the difference between x-rays and y-rays?

Answer 0

Y-rays are produced by nuclear reactions such as radioactive decay, but x-rays are produced when electrons decelerate rapidly.

Question 1

Wavelength of EM waves?

Answer 1

Radio - >10^6 to 10^-1
Microwaves - 10^-1 to 10^-3
Infrared - 10^-3 to 7x10^-7
Visible - 7x10^-7(red) to 4x10^-7(violet)
UV - 4x10^-7 to 10^-8
X-rays - 10^-8 to 10^-13
Y-rays - 10^-10 to 10^-16

Question 2

Frequency of EM waves?

Answer 2

R: 1 - 10^8
M: 10^8 - 10^12
I: 10^12 - 10^14
VL: 3.8x10^14 (red) - 7.5x10^14 (purple)
UV: 7.5x10^14 - 3x10^16
X: 3x10^16 - 3x10^19
G: 10^19<

Question 3

How is sound speed affected by density?

Answer 3

An increase in density leads to an increase in speed for a sound wave.
Decrease in velocity = bends towards normal
Increase in velocity = bends away from normal

Question 4

In water, how does a change in depth affect the speed of a wave?

Answer 4

Increase in depth = increase in speed = bends away from normal

Decrease in depth = decrease in speed = bends towards normal

Question 5

What happens to light when it enters glass?

Answer 5

Speed decreases, frequency stays the same therefore wavelength must also decrease.

Question 6

3 uses of radio waves?

Answer 6

TV and broadcasting radio, radio astronomy and MRI scans

Question 7

3 uses of microwaves?

Answer 7

Radar, mobile telecommunications and cooking

Question 8

3 uses of infrared?

Answer 8

Night vision goggles, remote controls and cooking

Question 9

2 uses of visible light?

Answer 9

Signalling and photography

Question 10

3 uses of UV?

Answer 10

Sterilisation, security marking and suntanning

Question 11

3 uses of x rays and gamma rays?

Answer 11

Sterilisation, medical imaging and medical treatment

Question 12

What is the wavelength of UV-A and what does it do?

Answer 12

Wavelength = 400-320nm

Very penetrating, cause skin to become wrinkled, or tanned (stimulates melanin production)

Question 13

What is the wavelength of UV-B and what does it do?

Answer 13

Wavelength = 320-280nm

Causes burning, cancer and helps to synthesise vitamin D

Question 14

What is the wavelength of UV-C and what does it do?

Answer 14

Wavelength = 280-100nm

Very damaging to cells, very high energy

Question 15

How does polarisation work?

Answer 15

Polaroid consists of long-chain molecules that absorb the energetic from the oscillating electric field. If molecules are vertically arranged, they absorb light waves which are vertically polarised, and so the waves become horizontally polarised.

Question 16

Define plane polarised?

Answer 16

Describes waves that oscillate in only one plane.

Question 17

How can you show that a microwaves transmitter emits plane polarised light?

Answer 17

Rotating a metal grille between the transmitter and the receiver. Metal rods in the grille will polarise the microwaves, and if they are already polarised then every 90degrees the transmitter should detect no microwaves.

Question 18

How do sunglasses work?

Answer 18

They reduce glare by selecting one polarisation of light waves only, so the amount of unpolarised?????????

Question 19

How does stress analysis of materials work?

Answer 19

In engineering, certain parts of a model may have high stress points. If the model is viewed through a Polaroid, areas of stress concentration show up where the coloured bands are closest together.

Question 20

What is an analyser?

Answer 20

A second polarising filter.

Question 21

A (of polarised light) = ?

Answer 21

AoCosΘ

Ao = orginal amplitude

Question 22

I (of polarised light) = ?

Answer 22

Io(Cosθ)^2