P13 - EM Waves

Question 1

EM spectrum in order (starting with longest wavelength)

Answer 1

Radio waves, Microwaves, Infrared, Visible light, Ultraviolet radiation, X rays and gamma radiation

Question 2

Radio waves wavelength

Answer 2

Kilometres

Question 3

Microwaves wavelength

Answer 3

Between kilometres and millimetres

Question 4

Infrared wavelength

Answer 4

Millimetres

Question 5

Visible light

Answer 5

Between millimetres and nanometres

Question 6

Ultraviolet radiation

Answer 6

Between Nanometres and picometres

Question 7

X-rays and gamma radiation

Answer 7

Picometres

Question 8

What properties do EM waves share?

Answer 8

They are all transverse waves
They can travel in a vacuum
They travel at 3 x 10^8 m/s

Question 9

What is increasing energy proportional to on the EM spectrum?

Answer 9

Increasing frequency

Question 10

What is increasing energy inversely proportional to on the EM spectrum?

Answer 10

Increasing wavelength

Question 11

Wave speed equation

Answer 11

Wave speed (m/s) = frequency (Hz) x Wavelength (m)

Question 12

P13 RP : To investigate which materials emit the most infrared radiation ( method)

Answer 12

Method
1. Fill a kettle with an appropriate amount of water
2. Boil the kettle
3. Place a heat proof mat underneath a Leslie Cube(each side with a different material)
4. Fill the Leslie Cube with boiling water
5. Measure 10cm from one side of the Leslie Cube ( directly in the middle)
6. From 10cm use an infra red thermometer to measure the temperature
7. Record the temperature
8. Change the side and repeat steps 5 to 7.

Question 13

The shorter the wavelength of the wave…

Answer 13

1. The more information carried
2. The shorter the range (greater absorption by the atmosphere)
3. The less they spread out.

Question 14

Which objects emit more infrared radiation?

Answer 14

Hotter objects

Question 15

Which surfaces absorb more infrared radiation?

Answer 15

Dark, Matte Black surfaces

Question 16

Which part of the EM spectrum do optical fibres use and why?

Answer 16

Optical fibres in communications systems usually use infrared radiation instead of visible light. This is because infrared radiation is absorbed less than visible light in the glass fibres.

Question 17

How do microwaves heat food?

Answer 17

Microwaves penetrate into food and are absorbed by the water molecules in the food, heating it

Question 18

Why can microwaves and radio waves be hazardous?

Answer 18

Because they penetrate people’s bodies and can heat the internal parts of the body.

Question 19

Why might children be more affected than adults by Electromagnetic radiation?

Answer 19

Because children have thinner skulls than adults there brains might be more affected by mobile phone radiation.

Question 20

What are optical fibres?

Answer 20

Very thin glass fibres. They are used to transmit signals carried by light or infrared radiation.

Question 21

Why can’t the light rays escape from the optical fibres?

Answer 21

When they reach the surface of the fibre, they are reflected back into the fibre.

Question 22

Differences between optical fibres and radio waves, microwaves

Answer 22

Optical fibres carry much more information as light has a much shorter wavelength than radio waves and so can carry more pulses of waves
Optical fibres are more secure because the signals stay in the fibre

Question 23

Hazards of Ultraviolet Waves

Answer 23

They are harmful to human eyes and can cause blindness
Harmful to skin- can cause sunburn and skin cancer

Question 24

Ways to protect against Ultraviolet Waves

Answer 24

Use skin creams to block UV waves
If in a sunbed wear special googles to protect your eyes

Question 25

Similarities between X-rays and gamma rays

Answer 25

Short wavelength end of the EM spectrum Carry much more energy per second than longer-wavelength EM waves

Question 26

Differences between X-rays and Gamma rays

Answer 26

• X-rays are produced when electrons or other particles moving at high speeds are stopped - X-ray tubes are used to produce X-rays gamma rays are produced by radioactive substances when unstable nuclei release energy • gamma rays have shorter wavelengths than X-rays, so they can penetrate substances more than X-rays can.

Question 27

Uses of Gamma rays

Answer 27

Exposing food to gamma rays kills 99% of disease- carrying organisms Exposing surgical instruments to gamma rays kills any bacteria on the instruments Doctors use Gamma ray therapy to destroy cancaerous tumours

Question 28

What is ionisation?

Answer 28

When atoms become charged because they lose electrons.

Question 29

What are examples of ionising radiation?

Answer 29

X-rays and gamma rays

Question 30

What can ionisation do?

Answer 30

If ionisation happens to a living cell, it can damage or kill the cell. For this reason, exposure to too many X-rays or gamma rays is dangerous and can cause cancer. High doses kill living cells, and low doses cause gene mutation and cancerous growth.

Question 31

Safety measures against ionising radiation

Answer 31

People who use equipment or substances that produce any form of ionising radiation (e.g., X-rays or gamma rays) must wear a film badge. If the badge shows that it is over-exposed to ionising radiation, its wearer is not allowed to continue working with the equipment for a period of time.

Question 32

How do X-rays travel through the body?

Answer 32

X-rays pass through soft tissue but are absorbed by bones (also teeth and some metal objects)

Question 33

What does the radiation dose depend on?

Answer 33

Type of radiation used How long the body is exposed to it The energy per second absorbed by the body from the radiation

Question 34

What is radiation dose measured in?

Answer 34

Sieverts (Sv)

Question 35

What is X-ray therapy?

Answer 35

Doctors use X-ray therapy to destroy cancerous tumours in the body.

Question 36

How does X-ray therapy work?

Answer 36

Thick plates between the X-ray tube and the body stop X-rays from reaching healthy body tissues. A gap between the plates allows X-rays through to reach the tumour

Question 37

X rays for therapy wavlength

Answer 37

Shorter in wavelength than X-rays used for imaging

Question 38

How do X rays work?

Answer 38

In an X-ray tube when fast-moving electrons hit a target.