Electromagnetic Spectrum

Question 1

What do all EM waves do?

Answer 1

They all transfer energy
They all are transverse waves
They all travel at the speed of light in a vacuum 3x10 to the 8 m/s)
They can all be reflected, refracted and diffracted

Question 2

What is the sequence of EM waves? What is light?

Answer 2

-Light is part if a continuous electromagnetic spectrum which includes: 
Radio Waves
Microwaves
Infrared (IR) 
Visible light
Ultraviolet 
X-Ray
Gamma Ray

Question 3

Describe Radio Waves

Answer 3

• Smallest Frequency: 105-1010Hz
• Largest wavelength: 103-10-2m
• Used for communications and broadcasting
• Sources: radio transmitters, TV transmitters
• Detectors: radio and TV ariels

Question 4

Describe Microwaves

Answer 4

• Frequency: 1010-1011Hz
• Wavelength: 10-2-10-3m
• Used for cooking, communications (mobile phones) and radar, satellite transmissions
• Sources: microwave transmitters and ovens.
• Detectors: microwave receivers

Question 5

Describe Infra-red (IR)

Answer 5

• Frequency: 1011-1014Hz
• Wavelength: 10-3-10-6m
• Used for infrared cookers, night vision equipment, heaters, television and stereo remote controls
• Sources: hot objects
• Detectors: skin, blackened thermometer, special photographic film

Question 6

Describe Visible light

Answer 6

• Frequency: 1014-1015Hz
• Wavelength: 10-6-10-7m
• Used for seeing, communications (optical fibres) and photography.
• Sources: luminous objects
• Detectors: the eye, photographic film, LDR

Question 7

Describe Ultraviolet (UV)

Answer 7

• Frequency: 1015-1016Hz
• Wavelength: 10-7-10-8m
• Used for fluorescent tubes and UV tanning lamps
• Sources: UV lamps and the Sun
• Detectors: skin, photographic film and some fluorescent chemicals

Question 8

Describe X-rays

Answer 8

• Frequency: 1016-1018Hz
• Wavelength: 10-8-10-10m
• Used for X-radiography, observing the internal structure of objects (e.g. at an airport) and materials and medical applications
• Sources: X-ray tubes
• Detectors: photographic film

Question 9

Describe Gamma rays

Answer 9

• Largest Frequency: 1018-1020Hz
• Smallest wavelength: 10-10-10-14m
• Used for sterilising food and medical equipment and food as well as radiotherapy.
• Sources: radioactive materials
• Detectors: Geiger-Müller tubes

Question 10

How does a microwave work?

Answer 10

1. The water molecules in the food absorb the microwaves.
2. Therefore the water particles have more energy and so mover faster and get excited, producing heat and so the food becomes heated.

Question 11

How are microwaves used for communications?

Answer 11

• Satellite communication (including satellite TV signals and satellite phones) use microwaves. But you need to use wavelengths of microwaves which can easily pass through the Earth’s watery atmosphere without being absorbed
  1. Microwaves can pass through the Earth’s atmosphere easily without being absorbed.
  2. Signal from a transmitter is transmitted into space to orbiting satellites and is picked up by the satellite receiver dish orbiting thousands of kilometres above the Earth
  3. From here it is passed on to other orbiting satellites or the signals are transmitted back to earth and is received by a satellite dish on the ground
  3. Messages sent to and from mobile phones are also carried by microwaves (microwaves can pass through brick, glass etc.)
• The microwaves used by mobile phones transmit much less energy than those used in a microwave oven
  4. Microwaves also used by remote-sensing satellites, to help ‘see’ through clouds and monitor oil spills, track the movement of ice bergs, and see how much of the rainforest is chopped down.

Question 12

How are radio waves used for communications?

Answer 12

1. Generated by a very rapidly oscillating current in a transmitter, same frequency as that of an ac current
2. Travel long distances as diffract around curved surface of Earth (hills etc.)
3. As they cross an ariel, they are detected and the information they carry can be received
4. TV and FM radio use radio waves with the shorter wavelengths to carry their signals. To get reception you must be in direct sight of the transmitter as the signal doesn’t bend around hills or travel far through buildings. 5. However still can be received at long distances from the transmitter as they are reflected from the ionosphere (an electrically charged layer in the Earth’s upper atmosphere). Medium-wave signals can also reflect form the ionosphere, depending on the atmospheric conditions and the time of day
   - Long-wave radio can be transmitted long distances because the long wavelengths diffract around the curved surface of the Earth and they also get around hills and into tunnels

Question 13

How is IR used?

Answer 13

1. All objects emit IR, the hotter an object the more energy it will emit as infra-red.
2. Toaster, and electrical fires also transfer heat energy by infra-red.
3. Used in remote controls, as they have a low penetrating power, not harmful and will therefor operate over small distances, so they are unlikely to interfere with other signals or waves.
4. Special camera designed to detect IR , create images even in absence of Visible light (searching for people trapped in collapsed buildings) and tracking criminals.
5. Too much exposure can cause skin burns (i.e. don’t touch hot objects)
6. IR photography can be used in daylight to detect: places where heat energy is leaking from buildings, tumours close to the skin (as tumours are warmer than surrounding tissue), areas of forest that are unhealthy (because dead plants are cooler than live ones)

Question 14

How is Visible Light used? What is the order of the colours?

Answer 14

1. Red, orange, yellow, green, blue, indigo, violet
2. Red light has longest wavelength and lowest frequency
3. Can be used in communications such as optical fibres, and can help see in inaccessible places (e.g. inside human body).
4. VL can also be detected by sensors in digital cameras, and can be used to take still photographs or videos.
5. VL from lasers can be used to read compact discs and barcodes.
6. White light is all colours in the visible spectrum added up.

Question 15

How is Ultraviolet Light used?

Answer 15

1. Fluorescence is a property of certain chemicals where ultraviolet radiation is absorbed and then visible light is emitted
2. Fluorescent lights use UV radiation to emit visible light, the are safe to use as nearly all the UV radiation is absorbed by a phosphor coating on the inside of the glass which emit visible light instead
3. Some chemicals glow or fluoresce when exposed to UV light so this is used in security markers (you can secretly label something)
4. Fluorescent tubes glow because the UV light they produce (mercury vapour inside the tube gives off UV rays when a current is passed through it) strikes a special coating on the inside of the tube, which then emits visible light.
5. Fluorescent bulbs are more energy efficient than incandescent bulbs/filament light bulbs, which is why they are often used in places like classrooms and offices where they are needed for a long period of time

Question 16

How are X-rays used?

Answer 16

• X-rays are used to view the internal structure of objects and materials, including our bodies
  1. X-rays can easily pass through soft body tissue without being absorbed, but not through bone or metal (as denser), so X-ray pictures can be taken to look at bones, (NO SURGERY :D), and helps to see dental fractures
  2. Used in industry to check internal structures of objects e.g. looking for cracks and faults in buildings and machinery, and at airports as part of the security check procedure (QUICK :D)
  3. To produce X-ray image, X-ray radiation is directed through the object or body onto a detector plate
  4. The brighter bits are where fewer X-rays get through and this is a negative image and the plate starts off all white
  5. Since exposure to X-rays can cause mutations which can lead to cancer, radiographers and patients are protected a much as possible by lead aprons and shields, and exposure to the radiation is kept to a minimum

Question 17

How are Gamma rays used?

Answer 17

• Highly penetrating rays
  1. Used to sterilise medical instruments as they kill all the microbes. This is better than trying to boil plastic instrument which might be damaged by high temperatures
  2. To kill microorganisms so that food will keep fresh for longer (by killing microbes) without having to freeze it, cook it or preserve it in some other way and the food is not radioactive afterwards and so ti is perfectly safe to eat
• Treat cancer using radiotherapy

Question 18

Why is UV light dangerous?

Answer 18

• Damages to surface cells and blindness:
  1. It is ionising and so it carries enough energy to knock electrons off atoms and thus can cause cell mutation or destruction and cancer
• Tanning:
  1. Dead skin may absorb UV light
  2. If penetrates to living skin, more vitamin D is produced (which is a good thing)
  3. Too much produces melanin which is a darker pigment and so makes us darker.
  4. As these cells die, as they naturally will they will move closer to the surface.
  5. Since darker surface absorb more UV light radiation, this exposes your living skin cells to more UV light
  6. Too much will cause them to burn and die and blister and peel off, leaving you with no protective layer.
• UV radiation may also cause skin cancer (ionising) and blindness.

Question 19

How can you protect yourself from UV light?

Answer 19

• Sunscreen with UV filters whenever you are out in the sun and stay out of strong sunlight to protect your skin from UV radiation. The sunscreen is absorbed by your dead cells, and so the UV light goes to those cells, preventing UV from reaching your living cells.
• Ozone in the Earth’s atmosphere absorbs large quantities of the Sun’s UV radiation. Amount of ozone is atmosphere is decreasing due to pollution, this may lead to increased numbers of skin cancers in the future

Question 20

Why are X-rays and Gamma rays dangerous?

Answer 20

1. Gamma rays, cancer and mutation
   -Radiation can ionise cells causing cellular damage. If absorbed into cell nuclei, can ionise DNA molecules:
   -If there is a high dose this can cause abnormal chemical reactions and can kill the cell.
   -If there is a small dose this can cause cell mutation, which could lead to the cell becoming cancerous or tissue damage.
   -The higher the exposure the higher the risk of cancer
   Alpha is the most ionising radiation and gamma is the least.
2. The ionising radiation can cause cell mutation or destruction, leading to tissue damage or cancer
3. Very high frequency waves, such as Gamma rays are ionising and carry much more energy than UV rays and so are much more damaging and can they can penetrate further into the body, than ultraviolet in ionising as they carry much more energy

Question 21

How can you protect yourself from X-rays (and Gamma rays)?

Answer 21

• Stand behind lead screens or wear protective clothing (lead shield as too dense for x-rays) and x-rays to only be directed in one area, leave the room and one off not too bad
• Gamma rays are only aimed carefully so that the cross at the exact location of the cancerous cells, at targeted cells so only there is the dose of gamma radiation high enough to damage or kill cells
• Radioactive sources of gamma rays should be kept in lead-lined boxes when not in use
• When people are exposed to gamma rays e,g, in medical treatment the exposure time should be as short as possible

Question 22

Why are microwaves dangerous and how can we be protected?

Answer 22

1. Microwaves have a similar frequency to the vibrations of many molecules, and so they can increase these vibrations
2. The result is internal heating which is the heating of molecules inside things (as in microwave ovens)
3. Microwaves can heat human body tissue (same as food), internally in this way
4. Therefore Microwaves have metal screens/shielding so that the microwaves are reflected and so are kept inside the oven to prevent microwaves from reaching the user.

Question 23

Why is Infrared dangerous and how can we be protected?

Answer 23

1. Can make surface molecules of any substance vibrate and so like microwaves they have this heating effect, however IR has a higher frequency and so it carries more energy
2. If human body is exposed to too much IR it can cause skin burns
3. To protect use insulating materials to reduce the amount of IR reaching your skin (e.g. oven gloves?)

Question 24

What is the trend in the EM spectrum?

Answer 24

Decreasing wavelength and increasing frequency (starting with Radio Waves)

Question 25

How is infrared used for heating and to monitor temperature?

Answer 25

1. IR is also known as heat radiation and electrical heaters radiate IR to keep us warm and things like grills use IR to cook food
2. IR is given out by all objects and the hotter the object the more IR radiation it gives out
3. The infrared radiation given out by objects can be detected by night vision equipment
4. The equipment turns it into an electrical signal, which is displayed on a screen as a picture
5. This allow things which would otherwise be hidden in the dark, to be seen

Question 26

How do light signals travel through optical fibres? How are they used in every day life?

Answer 26

1. As well as using visible light to look at things around is it can also be used for communication using optical fibres
2. Optical fibres work by bouncing waves off the sides of a very narrow core
3. The pulse of light enters the fibre at a certain angle at one end and is reflected again and again until it emerges at the other end
4. Optical fibres are being increasingly sued for telephone and broadband internet cables, replacing the old electric ones
5. They are also used for medical purposes to ‘see inside’ the body without having to operate and as twinkly lights at the ends of branches of artificial xmas trees

Question 27

What does an optical fibre do?

Answer 27

Carries data over long distances as pulses of light

Question 28

How is visible light used in photography?

Answer 28

1. Cameras use a lens to focus visible light onto a light-sensitive film or electronic sensor
2. The lens aperture controls how much light enters the camera (like the pupil of the eye)
3. The shutter speed determines how long the film or sensor is exposed to the light
4. By varying the aperture and shutter speed (and also the sensitivity of the film of sensor), a photographer can capture as much or as little light as they want in their photograph

Question 29

How can some EM radiation be harmful to people?

Answer 29

1. Some EM radiation mostly passes through soft tissue without being absorbed e.g. radio waves
2. Some types of radiation are absorbed and cause heating of cells e.g. microwaves
3. Some radiations can cause cancerous changes in living cells e.g. gamma rays can cause cancer

Question 30

How is the danger of EM radiation related to frequency?

Answer 30

1. The effects of EM radiation depend on its frequency. Th higher the frequency of EM radiation, the more energy it has and generally the more harmful it can be
2. In general waves with lower frequencies (like radio waves, which are harmless as far as we know) are less harmful than high frequency waves like X-rays and Gamma Rays
3. From a safety point of view, it is how radiation affects human tissue that is most vital