Physics - P1.6 - Electromagnetic Waves


P1.6.1 - The Electromagnetic Spectrum

  • Electromagnetic radiations - electric and magnetic disturbances, travel as waves, move energy from place to place
  • Electromagnetic spectrum - grouped by wavelength and frequency
  • Gamma rays - shortest wavelength, highest frequency, higher frequency = more energy transferred
  • Spectrum is continous and boundaries are approximate
  • Different wavelengths are reflected, absorbed or transmitted differently by different substances and types of surface
  • All have the same wavespeed through a vacuum = 300million m/s
  • Link waves to wavelength and frequency - v= f x λ
    • v - wavespeed - 300000000 m/s
    • f - frequency - Hz
    • λ - wavelength - m
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P1.6.2 - Light, Infrared, Microwaves and Radio Wav

  • Visible light - part of the electromagnetic spectrum, detectable by our eyes - different wavelengths = different colours, used for photography
  • Wavelength increases across spectrum from violet to red - white light = mixture
  • Infrared (IR) radiation given out by all objects, hotter = more emitted, remote controls use IR
  • Microwaves - used in communications, transmitters produce wavelengths able to pass through atmosphere, send signals to/from satellites and within mobile phone networks
  • Radiowaves - transmit radio/TV signals and carry mobile phone signals
  • Microwaves radiation and radio waves penetrate skin and absorbed by body tissue - heats internal organs - may cause damage
  • Infrared radiation absorbed by skin - too much will burn skin
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P1.6.3 - Communications

  • Alternating voltage applied, radio waves emitted from aerial, fr of radio waves = fr of alternating voltage, when pass over receiver aerial, alternating voltage caused - fr of alternating voltage = fr of radio waves
  • Radio and microwave spectrum divided into bands - each used differently
  • Shorter wavelength = more information carried = shorter range = less spread out
  • Mobile phones - communicate with local mobile phone mast - wavelengths on border between radio and microwaves
  • Some think radiation of mobile phones may affect the brain
  • Optical fibres - thin glass fibres used to transmit signals carried by visible light or infrared radiation - signal travels by repeated total internal reflection - useful: carry more information and more secure
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P1.6.4 - The Expanding Universe

  • Frequency of an object changes as it moves towards a point - Doppler effect
  • Moves away: wavelength increases, frequency decreases - moves towards: wavelength decreases, frequency increases
  • Galaxies - large collection of stars
  • Red shift - light observed from galaxies is shifted towards red end of the spectrum - wavelength increased, frequency decreased - moving away
  • Blue shift - light shifted to bue end of the spectrum - moving towards us - able to see these effects by observing dark lines in the spectra from galaxies
  • Further away galaxy = bigger red shift - most distant moving the fastest - true of all galaxies
  • All distant galaxies moving away from each other: universe is expanding
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P1.6.5 - The Big Bang

  • Big Bang theory - if the universe is expanding, it must have started with a massive explosion from a very small intial point
  • If universe began with the Big Bang - high energy gamma radiation was produced - as universe expands, it becomes lower-energy radiation
  • Cosmic Microwave Background Radiation (CMBR) - scientist found microwaves from every direction in space - the radiation produced by the Big Bang - Big Bang theory is the only theory to explain the exsistance of CMBR
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P1.6 - The Electromagnetic Spectrum

  • Radio Waves
  • Microwaves
  • Infrared Radiation
  • Visible Light
  • Ultraviolet Radiation
  • X-rays
  • Gamma Radiation
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