P13 New

Question 1

What type of waves are EM waves?

Answer 1

Transverse waves

Question 2

What do EM waves do?

Answer 2

All EM waves are transverse waves that transfer energy from a source to an absorber

Question 3

At what speed do all EM waves travel at? (In a vacuum or space)

Answer 3

300million m/s

Question 4

All EM waves travel at the same …

Answer 4

Speed, through a vacuum (space) or air

Question 5

What increases as you down the up the EM spec (radio to gamma waves) ?

Answer 5

The frequency increases and the wavelength decreases

Question 6

What is the order of the EM spec? Biggest to smallest wavelength

Answer 6

Radio waves, micro waves, infrared, visible light, ultra violet, X-ray, gamma ray

Question 7

What is white light? And why is it called that?

Answer 7

It is light from ordinary lamps and the sun

It has all the colours of the visible spectrum in it

Question 8

The hotter the object is the more …..

Answer 8

Infrared radiation it emits

Question 9

What is infrared radiation absorbed by?

Answer 9

It is absorbed by your skin and it can damage, burn or kill skin cells because it heats up the cell

Question 10

Why is infrared usually used in optical fibres instead of visible light?

Answer 10

This is because infrared radiation gets absorbed less than visible light in the glass fibres

Question 11

Why is infrared radiation usually used in electronics?

Answer 11

Because infrared can easily be produced and detected electronically

Question 12

What are infrared cameras used for?

Answer 12

You can see people and animals in the dark

Question 13

What are microwaves used for?

Answer 13

• People use microwaves for communications, for example satellite TV, because they can pass through the atmosphere and reach satellites above the Earth. Microwaves can also carry mobile phone signals.
• Microwave ovens heat food faster than ordinary ovens. This is because microwaves can penetrate into food and are absorbed by the water molecules in the food, heating it. The oven itself does not absorb microwaves as it does not contain any water molecules. It therefore does not become hot like the food it is cooking.

Question 14

Why can micro and radio waves be hazardous to human bodies?

Answer 14

Microwaves and radio waves can be hazardous because they penetrate people’s bodies and can heat the internal parts of the body.

Question 15

What are radio waves used for? And what frequencies do they range from?

Answer 15

• Radio wave frequencies range from about 300,000 Hz to 3000 million Hz (where microwave frequencies start). Radio waves are used to carry radio, TV, and mobile phone signals.
• You can also use radio waves instead of cables to connect a computer to other devices (bluetooth)

Question 16

What are carrier waves?

Answer 16

The waves used to carry any type of signal are called carrier waves.

Question 17

The shorter the wavelength of the waves …..

Answer 17

• The more infomation that they carry
• The shorter their range (due to increasing absorption by the atmosphere)
• The less they spread out

Question 18

Microwaves and radio waves of different wavelengths are used for different communications purposes. Examples include:

Answer 18

• Microwaves are used for satellite phone and TV links, and satellite TV broadcasting.This is because microwaves can travel between satellites in space and the ground. Also, they spread out less than radio waves do, so the signal doesn’t weaken as much.
• Radio waves of wavelengths less than about 1 metre are used for TV broadcasting from TV masts because they can carry more information than longer radio waves.
• Radio waves of wavelengths from about 1 metre up to about 100 m are used by local radio stations
• Radio waves of wavelengths greater than 100 m are used by national and international radio stations because they have a much longer range than shorter-wavelength radio waves.

Question 19

How is signal transmitted and detected?

Answer 19

1) An oscillator supplies carrier waves to the transmitter in the form of an alternating current

2) The audio signal is supplied to the transmitter where it’s used to modulate the carrier waves.

3) The modulated carrier waves from the transmitter are supplied to the transmitter aerial. The varying alternating current supplied to the aerial causes it to emit radio waves that carry the audio signal.

4) When the radio waves are absorbed by a receiver aerial, they induce an alternating current in the receiver aerial, which causes oscillations in the receiver.

5) The receiver circuit separates the audio signal from the carrier waves. The audio signal is then supplied to a loudspeaker, which sends out sound waves similar to the sound waves received by the microphone in the radio station.

Question 20

What are optical fibres? And how do they compare to radio and microwaves

Answer 20

Optical fibres are very thin glass fibres. They are used to transmit signals carried by light or infrared radiation. The light rays can’t escape from the fibre. When they reach the surface of the fibre, they are reflected back into the fibre.

• 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 21

What happens when chemicals absorb ultraviolet waves?

Answer 21

They emit visible light

Question 22

How can ultraviolet be harmful? (UV light)

Answer 22

-Ultraviolet waves are harmful to human eyes and can cause blindness.

-Ultraviolet waves are harmful to your skin. For example, too much UV directly from the Sun or from a sunbed can cause sunburn and skin cancer.

Question 23

What are some properties of X-rays and Gamma rays?

Answer 23

They carry much more energy per second than longer wavelength EM waves and they can pass through objects if they are not too dense and thick

Question 24

How are Gamma and X-rays produced?

Answer 24

• 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

Question 25

How can Gamma rays be used?

Answer 25

• Killing harmful bacteria - exposing food to gamma rays destroys 99% of disease carrying organisms, it can also be used to sterelise surgical equipment
• Killing cancer cells - Doctors and medical physicists use gamma-ray therapy to destroy cancerous tumours.

Question 26

What is ionisation? And why is it dangerous?

Answer 26

It is when X-rays and gamma rays knock of electrons out of atoms which makes them positively charged and if this happens at high doses to a living cells it can kill the cell. Lower doses of Ionising radiation can cause cancer as it can mutate living cells.

Question 27

What is radiation dose? Whats it measured in etc.

Answer 27

• Radiation dose is a measure of the risk of harm from the body being exposed to radiation.
• The risk depends on how harmful the type of radiation is and the total amount of radiation absorbed.
• Radiation dose is measured in Sieverts

Question 28

What do X-rays do? And why are they suited for medical imaging?

Answer 28

• X-rays pass through soft tissue ( like skin and muscles so a contrast medium has to be used to scan the inner parts of organs for example ), but they are absorbed by bones, teeth and metal objects that are not too thin
• This means that any breaks or fractures can be found

Question 29

What’s a contrast medium?

Answer 29

An organ that consists of soft tissue can be filled with a substance called a contrast medium that absorbs X-rays easily. This enables the internal surfaces in the organ to be seen on the radiograph.

Question 30

What stops x-ray and gamma?

Answer 30

Thick layers of lead - can be used to prevent x-rays from reaching dufferent parts of the body that you dont want to scan

Question 31

What is X-ray therapy? And why is it used?

Answer 31

• Doctors use X-ray therapy to destroy cancerous tumours in the body.
• Thick plates between the X-ray tube and the body stop X-rays from reaching healthy body tissues.
• The X-rays used for therapy carry much more energy than X-rays used for imaging. Low-energy X-rays are suitable for imaging because they are absorbed by bones and teeth but they pass through soft tissue and gaps such as cracks in bones. Low-energy X-rays do not carry enough energy to destroy cancerous tumours.

Question 32

How can a radio wave be produced?

Answer 32

Radio waves can be produced by oscillations in electrical circuits.

Question 33

What happens when radio waves are absorbed?

Answer 33

When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit.