P13 - EM Waves

Question 1

What are electromagnetic waves and what are the properties that they all share?

Answer 1

The direction of oscillation is 90 degrees. They are all transverse waves. They all travel at 3 x 10^8 m/s. They are all able to travel through a vacuum as they do not need a medium.

Question 2

How do you calculate the speed of electromagnetic waves?

Answer 2

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

Question 3

Name the waves of the electromagnetic spectrum in order.

Answer 3

Radio waves, microwaves, infrared, visible light, ultraviolet radiation, x-rays and gamma radiation.

Question 4

What are the sources of radio waves?

Answer 4

• Phones
• Radio towers

Question 5

What are the effects of radio waves on the body?

Answer 5

Radio waves pass through the body without being absorbed.

Question 6

What is one main use of radio waves and how does it work?

Answer 6

When you use a mobile phone, radio waves carry signals between your phone and the nearest mobile phone mast. The waves used to carry any type of signal are called carrier waves.

Question 7

Why are radio waves suited to its uses?

Answer 7

Longer wavelength radio waves travel much further than short wavelength radio waves and can be used to send signals around the world. Short wavelength radio waves need a clear line of sight between the transmitter and receiver, e.g. Bluetooth.

Question 8

What are sources of microwaves?

Answer 8

Stars

Question 9

What are the effects on the body of microwaves?

Answer 9

Some wavelengths of microwaves can be absorbed, causing heating of cells , which may be dangerous.

Question 10

What is one main use of microwaves and how does it work?

Answer 10

Satellite communication:
A signal is sent into the atmosphere. Because of their short wavelength, microwaves are transmitted through the atmosphere. The signal reflects from a satellite and is sent back to Earth. It is received by a satellite dish on the ground.

Question 11

Why are microwaves suited to their uses?

Answer 11

Microwaves have a short wavelength, which allows them to pass through the atmosphere and reach satellites, making them ideal for long distance communication.

Question 12

What are sources of infrared radiation?

Answer 12

Infrared radiation is given off by all objects, the hotter the object the more infrared radiation is given off.

Question 13

What are the effects on the body of infrared radiation?

Answer 13

Infra-red radiation is mostly reflected or absorbed by the skin, causing some heating too. It can cause burns if the skin gets too hot.

Question 14

What is one main use of infrared radiation and how does it work?

Answer 14

Infra-red cameras can be used to detect the IR radiation given off by objects and monitor their temperature. They turn the infra-red wave into an electrical signal , which is then turned into an electrical signal and displayed on a screen. The hotter the object is, the brighter it will appear in the image.

Question 15

Why is infrared radiation suited to its uses?

Answer 15

Infrared radiation is given off by all objects and the amount increases with temperature, so it is ideo for detecting heat and monitoring temperature changes in things like the human body or food.

Question 16

What are the sources of visible light?

Answer 16

Light sources such as lamps, the sun or LEDs.

Question 17

What are the effects on the body of visible light?

Answer 17

Visible light is mostly absorbed or reflected by the skin but can cause some heating effects.

Question 18

What is one main use of visible light and how does it work?

Answer 18

Communication through optical fibres:Light signals are sent along optical fibres, which are thin glass or plastic tubes. These carry information over long distances as pulses of light. Light bounces iff the sides if a very narrow core as it travels. The pulse of light enters at one end and is repeatedly reflected until it emerges at the other end. Used in telephone and internet connections.

Question 19

Why is visible light suited to its uses?

Answer 19

Visible light can be reflected inside optical fibres, allowing it to carry information over long distances with little loss. This makes it ideal for high speed communication like internet.

Question 20

What are sources of ultraviolet radiation?

Answer 20

Un radiation is produced by the sun and UV lamps

Question 21

What are the effects on the body of ultraviolet light?

Answer 21

At the higher frequency of UV radiation, it can be ionising which can cause damage to the cells in the body, and can cause cancer as a result.

Question 22

What is one main use of ultraviolet light and how does it work?

Answer 22

Fluorescence is a property of certain chemicals, where UV radiation is absorbed and visible light is emitted. Security pens can be used ot mark property and when UV light is shone onto the ink it will glow, allowing stolen property to be identified.

Question 23

Why is ultraviolet light suitable for its uses?

Answer 23

Stolen property can be identified by the use of security pens.

Question 24

What are sources of x-rays?

Answer 24

X-rays are produced when electrons or other particles travelling at high speed collide with a metal target—X-ray tubes are used to produce X-rays.

Question 25

What are the effects on the body of x-rays?

Answer 25

Exposure to X-rays can cause cell damage, similar to UV radiation, and so radiographers and patients are protected as much as possible by using either lead aprons or shields and exposure to the radiation is kept to a minimum. It is ionising.

Question 26

What is one main use of x-rays and how does it work?

Answer 26

X-rays can be used to view the internal structure of objects and materials, such as broken bones or cracks in metal objects. To do this X-rays are directed through the object or the body towards a detector plate. The X-rays will be absorbed by dense materials, such as bone or metal, but will pass through less dense materials, such as muscle or skin, to produce an image on the detector screen.

Question 27

Why are x-rays suitable for their uses?

Answer 27

X-rays are able to be used to identify broken bones in the body, because they cannot completely pass through dense material.

Question 28

What are the sources pf gamma radiation?

Answer 28

Gamma rays are produced by radioactive substances when unstable nuclei release energy.

Question 29

What are the effects on the body of gamma radiation?

Answer 29

Gamma rays are ionising, and so can cause damage to the cells of the body, which as a result can cause cancer.

Question 30

What is one main use of gamma radiation?

Answer 30

Gamma rays can be used to sterilise medical instruments or food by killing the microbes on these objects. This is better than boiling as it does not damage the objects and they are safe to use after being treated.

Question 31

Why is gamma radiation suited for its use?

Answer 31

Gamma rays are good for sterilising medical equipment because it is better than boiling as it does not damage the objects and they are safe to use after being treated.

Question 32

What is the method for the absorption and emission of infrared radiation practical?

Answer 32

1. Firstly place a heat proof mat on a flat surface such as a table where this experiment can be done. 2. Next take your Leslie cube and place it on the heat proof mat. 3. Begin boiling a kettle with water inside. 4. Once the water in the kettle has finished boiling, pick up the kettle and bring it over to the Leslie cube. 5. Open the tap on the Leslie cube and then start pouring the water from the kettle to the brim so that it is full of water. 6. Once you have finished pouring make sure to put the tap on the Leslie cube, so that no steam can escape. 7. Finally, take your infra-red thermometer and measure the temperature on the different surfaces at the same distance. To make sure the infra-red thermometer is the same distance away from the Leslie cube every time use the 30 cm ruler to make relatively accurate measurements. 8. Then plot your results on a suitable graph.

Question 33

How does mobile phone messaging work?

Answer 33

- User types message into his mobile phone and clicks send - Message travels to a mobile phone tower near sender's phone - Tower sends message to short message service centre (SMSC) - SMSC formats message - SMSC sends message as packet of data to phone tower near recipient's phone - Tower sends message ro recipient's phone

Question 34

What do shorter wavelength for radio waves mean?

Answer 34

- More information can be carried - The shorter the range (greater absorption by the atmosphere) - The less they spread out

Question 35

Compared with radio waves and microwaves, optical fibres:

Answer 35

- Carry much more information as light has a much shorter wavelength than radio waves, and so can carry more pulses of waves. - Are more secure because the signals stay in the fibre.

Question 36

What is optical fibre and how does it work?

Answer 36

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.

Question 37

What is a carrier wave?

Answer 37

Carrier waves are waveforms that have been modified to transmit information.

Question 38

How can we protect ourselves from UV light?

Answer 38

- Use skin creams that block UV light (sun cream) - Cover skin with clothes - Don't spend too long on a sun-bed - Wear UV filter sunglasses

Question 39

What can be used to protect yourself from x-rays and gamma rays?

Answer 39

Lead

Question 40

What is radiation dose?

Answer 40

A measure of the risk of harm resulting from an exposure of the body to ionising radiation.

Question 41

What is radiation dose measured in?

Answer 41

It is measured in Millisieverts (mSv)

Question 42

What precautions are taken when using x-rays?

Answer 42

- Patients are limited to the number of x-rays they are allowed to have. - Shielded walls containing lead are built into all x-ray rooms to protect people outside the room. - Only trained specialist staff (radiographers) can use x-ray machines.

Question 43

State one advantage and one disadvantage of a Ct Scanner in comparison with an ordinary X-ray machine.

Answer 43

Advantage: A CT scan distinguishes between different types of soft tissue and can give a three-dimensional image. Disadvantage: The radiation dose from a CT scan is much greater than from an ordinary X-ray imaging machine and Ct Scanners are much more expensive to buy and operate than ordinary X-ray machines.