Physics P6

  • Created by: abbiedye
  • Created on: 29-07-18 20:44

What are transverse waves?

  • In transverse waves, the oscillations (vibrations) are perpendicular to the direction of energy transfer
  • Include: all electromagnetic waves (light), ripples and waves in water, and a wave on a string
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What are longitudinal waves?

  • In longitudinal waves, the oscillations are parallel to the direction of the energy transfer
  • Sound waves in air
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How do you calculate wave speed?

  • The speed at which energy is being transferred
  • wave speed = frequency x wave length
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When a wave meets a boundary

Three things can happen

  • The wave is absorbed by the second material
  • The wave is transmitted through the second material
  • The wave is reflected
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What are electromagnetic (EM) waves?

  • Transverse waves
  • Travel at the same speed through air or a vacuum (space)
  • They vary in wavelength from around 10^-15 m to more than 10^4m
  • We group them based on their wavelength and frequency
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What is the spectrum of waves?

  • Radio waves - 1m to 10^4m
  • Microwaves - 10^-2m
  • Infrared - 10^-5m
  • Visible Light - 10^-7m
  • Ultra violet - 10^-8m
  • X-rays - 10^-10m
  • Gamma rays - 10^-15m

DIFFERENT PROPERTIES

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What is refraction?

  • Refraction = waves changing direction
  • Ray diagrams show the path of a wave
  • You can also explain refraction using wavefront diagrams
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How are radiowaves made?

  • EM waves are made up of oscillating electric and magnetic fields
  • Alternating currents (ac) are made up of oscillating charges. As the charges oscillate, they produce oscillating electric and magnetic fields i.e electromagnetic waves
  • Radio waves - ac in an electrical circuit
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How are radio waves used for communication?

  • Long-wave radio - can be transmitted halfway round the world
  • Short-wave radio - received at long distances from the transmitter
  • Bluetooth - short distances
  • Medium - waves
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What are the uses of microwaves?

  • Satellites - signals from a transmitter to a satellite, sent and received from a long distance
  • Microwaves ovens - microwaves need to be absorbed by water molecules, microwaves penetrate a few cms into food before being absorbed
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What can infrared radiation be used for?

  • Infrared cameras - detect radiation and monitor temperature
  • Absorbing IR radiation causes objects to get hotter - food can be cooked
  • Electric heaters work in the same way
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What are more uses of EM waves?

  • Fibre optic cables use visible light to transmit data
  • Ultraviolet radiation gives you a suntan
  • X-rays and gamma rays are used in medicine - x-rays and treating cancer
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How can you investigate infrared radiation?

  • You can investigate emission with a Leslie cube
  • You can investigate absorption with the melting wax trick
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Why are some EM radiation sources harmful?

  • Low frequency - don't transfer much energy and pass through tissue
  • High frequency - transfer lots of energy and cause a lot of damage
  • UV radiation - damages surface cells and skin cancer
  • X-rays and gamma rays - ionising and gene mutation and destruction
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How can you measure risk of radiation?

  • Measured in the radiation dose sieverts
  • It measures the risk of harm from the body being exposed to radiation
  • It is not a measure of the amount of radiation that has been absorbed - risk = amount and how harmful
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