P13

Electromagnetic spectrum

Electromagnetic waves are electric and magnetic disturbances used to transfer energy from a source to an absorber. 

  • Electromagnetic waves don't transfer matter. The energy they transfer depends on their wavelength. The electromagnetic spectrum is continuous.
  • Waves from different parts of the spectrum have different wavelengths. 

All EM waves travel at a speed of 3.0 x 10^8m/s (speed of light) through a vacuum or space.

wave speed, v (m/s) = frequency, f (Hz) x wavelength, λ (m)

  • The shorter the wavelength of the waves, the higher the frequency. Wave energy increases as frequency does. So, as wavelength decreases along the EM spectrum from radio waves to gamma rays, energy and frequency increase.
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Infrared, microwaves, radio waves

  • White light contains all the colours of the visible spectrum
  • Used in film and digital cameras 

Infrared radiation - used for carrying signals from remote control handsets and inside optical fibres

Also used to see people in the dark

Microwaves are used to carry satellite TV programmes and phone calls

Radio waves are used for radio and tv broadcasting

Mobile phone radiation is microwave radiation 

Microwaves and radio waves can heat the internal parts of people's bodies.

Infrared radiation can cause skin burns

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Communications

Radio waves of different frequencies are used for different purposes beacuse the wavelength of waves affect:

  • how far they travel
  • how much they spread
  • how much info they carry

The longer the wavelength, the longer the range the radio station has 

Further research is needed to evaluate whether mobile phones are safe to use

  • Carrier waves are waves that are used to caryy information, by varying their amplitude

Oscillators supplies waves to a transmitter using an AC. 

  • Optical fibres are thin transparent fibres that are used to transmit communication signals by light and infrared radiation
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Ultraviolet waves, X-rays and gamma rays

  • Ultraviolet waves have a shorter wavelength than visible light and can harm the skin and eyes

They are used in security marker pens.

X-rays are used in hospitals to make X-ray images. They are produced when electrons or other particles moving at a high speed are stopped

Gamma rays are used to kill harmful bacteria in food, to sterilise surgical euipment and to kill cancer cells. They are produced by radioactive substances when unstable nuclei release energy

Ionising radiation makes uncharged atoms charged.

Gamma rays have shorter wavelengths so can penetrate substances more

  • X-rays and gamma rays damage living tissue when they pass through it.
  • Too much exposure can cause cancer, killing living cells
  • People who use equipment causing ionising radiation must wear a film badge
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X-rays in medicine

X-rays are used in hospitals:

  • To make images of internal body parts
  • To destroy tumours at or near the body surface

They are absorbed more by bones and teeth than by soft tissues

  • X-rays from a tube are directed at the patient
  • They pass through soft tissue and absorbed by teeth and bones. The parts of the film the X-rays reach become darker than the other parts.
  • The radiograph shows a 'negative image' of the bones

Lead plates between the tube and the patient stop X-rays reaching other parts of the body

Damage of radiation depends on:

The type of radiation used, how long the body is exposed to it and the energy per second absorbed from the. radiation.

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