Electromagnetic Waves

Question 1

What are electromagnetic waves?

Answer 1

Electric and magnetic disturbances that can be used to transfer energy from a source to an absorber.
They do not transfer matter. They energy they transfer depends on the wavelength of the waves. This is why waves of different wavelengths have different affects.

Question 2

List the electromagnetic spectrum in order of long wavelength to shorter wavelength.

Answer 2

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

Question 3

Why is the speed of electromagnetic waves in a vacuum?

Answer 3

3.0 x 10*8 m/s (300 million m/s)

Question 4

What is the wave speed equation?

Answer 4

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

Question 5

What does the wave speed equation tell us?

Answer 5

Since electromagnetic waves all have the same speed, the shorter the wavelength of the waves, the higher the frequency. The energy of the waves increases as the frequency increases.
So as the wavelength decreases, the energy and frequency of the waves increase.

Question 6

What is white light?

Answer 6

Light from ordinary lamps and from the sun is called white light. This is because it has all the colours of the visible spectrum in it. The wavelength increases across the spectrum as you go from violet to red.

Question 7

What is infrared radiation?

Answer 7

All objects emit infrared radiation.
The hitter an object is, the more infrared radiation it emits.
Infrared radiation is absorbed by your skin. It can damage, burn, or kill skin cells because it heats up the cells.

Question 8

Uses of infrared radiation?

Answer 8

Optical fibres in communication systems instead of visible light. This is because infrared radiation is absorbed less than visible light in the class fibres.
Remote control handsets. They transmit signals carried by infrared radiation. Sends off a sequence of infrared pulses.
Infrared scanners are used in medicine to detect infrared radiation emitted from hot spots on the body surface. These hit areas can mean the tissue underneath is unhealthy.
To see people and animals in the dark.

Question 9

What are microwaves?

Answer 9

They have a shorter wave length than radio waves.

Question 10

What are the uses of microwaves?

Answer 10

Communications because they can pass through the atmosphere and reach satellites above the Earth. They also carry mobile phone signals.
They often heat food faster than ordinary ovens. This is because the microwave can penetrate into food and are absorbed by the water molecules in the food, heating it.

Question 11

What are radio waves?

Answer 11

They are used to carry radio, TV, and mobile phone signals.

Question 12

What is the use of radio waves?

Answer 12

Used instead of cables to connect a computer to other devices such as a printer or a computer mouse. Eg Bluetooth enabled devices.

Question 13

Why can micro waves and radio waves be hazardous?

Answer 13

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

Question 14

What are carrier waves?

Answer 14

The waves used to carry any type of signal are called carrier waves. They could also be radio waves, micro waves, infrared radiation, or visible light. The type of wave used to carry a signal depends on how much information is in the signal and the distance the signal has to travel.

Question 15

In the radio and microwave spectrum, what happens as the wavelength gets shorter?

Answer 15

The shorter the wavelength of the wave:
The more information they can carry
The shorter their range (due to increasing absorption by the atmosphere)
The less they spread out

Question 16

What are the uses of microwaves of different wavelengths?

Answer 16

Used for satellite phone and TV links, and satellite TV broadcasting. This is because microwaves can travel between satellites in skate and the ground. Also, the spread out less the radio waves do, so the signal doesn’t weaken as much.

Question 17

What are the uses of radio waves with differing wavelengths?

Answer 17

Short wavelengths are used for tv broadcasting from tv masts because they can carry more information than longer wavelengths.
From one metre to one hundred metres are used by local radio stations and for the emergency devices because there range is limited in the area around the transmitter.
Radio waves with wavelengths greater than one hundred are used by national and international radio stations because they have a much longer range than shorter-wavelength radio waves.

Question 18

How do carrier waves work?

Answer 18

An oscillator supplies carrier waves to the transmitter in the form of an alternating current (a current that repeatedly reverses its direction).
The audio signal is supplied to the transmitter where it is used to modulate carrier waves.
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.
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. The frequency of the oscillations is the same as the frequency of radio waves.
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 soundwaves received by the microphone in the radio station.

Question 19

What is optical fibre communication?

Answer 19

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 to the fibre.

Question 20

Compare optical fibres with radio waves and microwaves.

Answer 20

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

Question 21

How do x-rays work?

Answer 21

When the x ray tube is switched on, x rays from the tube pass through the part of the patients body under investigation.
X-rays pass through soft tissue, but they are absorbed by bones, teeth, and metal objects that are not too thin. The parts of the film or the detector that the x-rays reach become darker than the other parts. So the bones appear lighter than the surrounding tissue, which appears dark.

Question 22

How can you use x-rays for soft tissue?

Answer 22

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. Eg the patient may be given a barium meal.

Question 23

Why are lead plates used during x-rays?

Answer 23

Lead plates between the tube an the patient stop x-rays reaching other parts of the body. The x-rays reaching the patient pass through a gap between the plates. Lead is used because it is a good absorber of x-rays.

Question 24

what is a flat-panel detector?

Answer 24

A flat-panel detector is a small screen that contains a charge-coupled device (CDD). The sensors in the CDD convert x-rays to light. The light rays then create electronic signals in the sensors that are sent to a computer, which displays a digital x-ray image.

Question 25

What is radiation dose measured in?

Answer 25

Sieverts (Sv)
or Millisieverts (mSv0

Question 26

What does radiation dose depend on?

Answer 26

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

Question 27

Why can radiation be dangerous?

Answer 27

X-rays, gamma rays, and the radiation from radioactive substances all ionise substances they pass through.
High doses of radiation kill living cells. Low doses can cause gene mutation and cancerous growth.

Question 28

What is x-ray therapy?

Answer 28

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 tissue. A gap between the plates allows X-rays through to reach the tumour. X-rays for therapy are shorter in wavelength than X-rays used for imaging.

Question 29

Explain the X-rays used for X-ray therapy.

Answer 29

They carry much more energy than X-rays used for imaging. Low energy X-rays do not carry enough energy to destroy cancerous tumours.