The electro-magnetic spectrum

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The electro-magnetic spectrum
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Key facts

• All the waves travel at the same speed around
  300 000 km/s

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Key facts

• All the waves travel at the same speed around
  300 000 km/s
• All the waves are transverse waves

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Key facts

• All the waves travel at the same speed around
  300 000 km/s
• All the waves are transverse waves
• All the waves can be reflected and refracted

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Key facts

• All the waves are transverse waves
• All the waves can be reflected and refracted
• The longest waves are the radio waves

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Key facts

• All the waves can be reflected and refracted
• The longest waves are the radio waves
• The shortest waves are the gamma waves

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Key facts

• The longest waves are the radio waves
• The shortest waves are the gamma waves
• The shorter the wavelength, the higher the
  frequency

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Key facts

• All the waves travel at the same speed around
  300 000 km/s
• All the waves are transverse waves
• All the waves can be reflected and refracted
• The longest waves are the radio waves
• The shortest waves are the gamma waves
• The shorter the wavelength, the higher the
  frequency

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Key facts

• The shorter the wavelength the more dangerous the
  wave!!!!!!

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Key facts

• All waves shorter than visible light can cause
  cancer.
• UV - light - sun burn and skin cancer
• X-rays can cause cancer (that is why the dentist
  leaves the room when she X-rays your teeth)
• Gamma rays are the most dangerous they can kill
  ALL living things and cause cancer.
• We are bombarded by gamma rays coming from the
  sun every day!

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Digital and Analogue Signals

• Using optical fibres

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Using optical fibres

• Light and infrared radiation can be sent down an
  optical fibre.
• One optical fibre cable can carry 40 000
  telephone calls at the same time!

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Using optical fibres

• Advantages of optical fibres
• Light can travel round corners in an optical
  fibre. So unlike a microwave transmission it is
  not restricted to travelling in a straight line.

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Using optical fibres

• Advantages of optical fibres
• Light passes along an optical fibre with very
  little energy loss. Unlike a copper cable the
  signal does not need frequent amplification.

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Digital and analogue signals
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Digital and analogue signals

• Digital signals can be sent down optical fibres
• A digital signal can only have certain values,
  usually 0 or 1
• An analogue signal carries information by
  continuously changing its amplitude or frequency.

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Digital and analogue signals

• Noise distorts all signals during transmission.
  It cannot be removed from analogue signals.
• Digital signals can easily be restored to their
  original condition.
• This gives digital signals clearer sound and
  pictures.

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Digital and analogue signals

• A CD is a digital recording system.

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Digital and analogue signals

• A vinyl record is an analogue recording system.