Electromagnetic radiation

The electromagnetic spectrum
1. The pattern produced when white light shines through a prism is called the visible spectrum.
2. The prism separates the mixture of colours in white light into the different colours red, orange, yellow, green, indigo and violet.
3. In fact, visible light is only part of the electromagnetic spectrum. It’s the part we can see.
The electromagnetic spectrum and its uses
1. spectrum and its uses
  1. gamma radiation
    1. killing cancer cells
  2. x-rays
    1. medical images of bones
  3. ultraviolet radiation
    1. sunbeds
  4. visible light
    1. seeing
  5. infrared radiation
    1. optical fibre communication
  6. microwaves
    1. cooking
  7. radio waves
    1. television signals
  8. lowest frequece
  9. highest fequenc
  10. longest
  11. shortest
2. All types of electromagnetic radiation travel at exactly the same speed through a vacuum, 300,000 km/s.
Photons and ionisation
1. Electromagnetic radiation comes in tiny ‘packets’ called photons.
2. The photons deliver different quantities of energy, with radio photons delivering the smallest amount, and gamma photons delivering the greatest amount of energy.
3. A higher frequency of electromagnetic radiation means more energy is transferred by each photon.
4. If the photons have enough energy, they can break molecules into bits called ions. This is called ionisation. These types of radiation are called ionising radiation. This radiation can remove electrons from atoms in its path.
5. In the electromagnetic spectrum only the three types of radiation, which have the photons with most energy, are ionising. These are ultraviolet, X-rays and gamma rays.
Damaging to health - Higher tier
1. The ions produced when ionising radiation breaks up molecules can take part in other chemical reactions. If these chemical reactions are in cells of your body, the cells can die or become cancerous. This is the reason that ionising radiation can be damaging to health.
Energy and intensity
1. The intensity of electromagnetic radiation is the energy arriving at a square metre of surface each second. This depends on two things: the energy in each photon, and the number of photons arriving each second.
2. To have the same intensity, a beam of red light would need ten times as many photons as a beam of ultraviolet, and a beam of microwaves would need a million times as many.
3. Energy of 1 ultraviolet photon = Energy of 10 red photons = Energy of 1,000,000 microwave photons
Absorption of radiation - Higher tier
1. All forms of electromagnetic radiation deliver energy. This will heat the material that absorbs the radiation. The amount of heating depends on the intensity of the radiation, and also the length of time the radiation is absorbed for.
Electromagnetic radiation
1. An object which gives out electromagnetic radiation is called a source of radiation. Something which is affected by the radiation is a detector.
2. Lower intensity of radiation
  1. urther from the source, the detector receives a lower intensity of radiation.
  2. As the photons spread out from the source, they are more thinly spread out when they reach the detector. The intensity may also decrease with distance due to partial absorption by the medium it travels through.
Ionising radiation
1. Ionising radiation can break molecules into smaller fragments. These charged particles are called ions. As a result, ionising radiation damages substances and materials, including those in the cells of living things. The ions themselves can take part in chemical reactions, spreading the damage.
2. Ionising radiation includes:
  1. ultraviolet radiation, which is found in sunlight
  2. x-rays, which are used in medical imaging machines
  3. gamma rays, which are produced by some radioactive materials.
3. Non-ionising radiation
  1. Not all types of electromagnetic radiation are ionising. Radio waves, light and microwaves are among them.
4. Microwaves
  1. Microwaves are used to heat materials such as food. The molecules in the material absorb the energy delivered by the microwaves. This makes them vibrate faster, so the material heats up.
  2. The heating effect increases if:
    1. the intensity of the microwave beam is increased
    2. the microwave beam is directed onto the material for longer.
    3. So you need to cook food for longer in a less powerful microwave oven. This is why they have power ratings, and food labels recommend different cooking times depending on this

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	Criado por jakeogilvie mais de 11 anos atrás