WAVES

• Wavelength


  Distance between the same points on two consecutive waves

  
• Amplitude


  Distance from equilibrium line to the maximum displacement (crest or trough)
• Frequency


  The number of waves that pass a single point per second
• Period


  The time taken for a whole wave to completely pass a single point
• Transverse waves


  • the wave oscillates perpendicular (at right angles) to the direction of energy transfer

  
• Longitudinal waves(sound waves)


  • Have compressions and rarefactions
  • the wave oscillates parallel to the direction of energy transfer

  
• For both transverse and longitudinal waves, the wave moves and not whatever it passes through

  
• Measuring velocity of sound in air

  1. Make a noise at ~50m from a solid wall, and record time for the echo to be heard, then use speed = distance/time

  2. Have two microphones connected to a datalogger at a large distance apart, and record the time difference between a sound passing one to the other – then use speed = distance/time
• Measuring velocity of ripples on water surface

  1. Use a stroboscope, which has the same frequency as the water waves, then measure distance between the 'fixed' ripples and use v = fλ

  2. Move a pencil along the paper at the same speed as a wavefront, and measure the time taken to draw this line – then use speed = distance/time

  
• Electromagnetic waves are transverse waves
• Electromagnetic waves do not need particles to move
• In space, all electromagnetic waves have the same velocity (speed of light)
• Electromagnetic waves can transfer energy from a source to absorber
• Our retina can only detect visible light, a small part of the entire EM spectrum
• Refraction


  • If entering a denser material, it bends towards the normal
  • If entering a less dense material, it bends away from normal
• Substances will absorb, transmit, refract or reflect certain EM waves depending on wavelength

  
• When light enters a denser medium, it slows down
• Shorter wavelengths slow down more than longer wavelengths
• When refracting, the speed decreases and wavelength decreases too in denser material</b>
• Radio waves


  • Produced by oscillations in electrical circuits
  • When radio waves are absorbed they create an alternating current, AC, at the same frequency as the radio waves

  
• Atoms and EM radiation


  1. When electrons change orbit (move closer or further from the nucleus)

  2. When electrons move to a higher orbit (further from the nucleus), the atom has absorbed EM radiation

  3. When the electrons falls to a lower orbit (closer to the nucleus), the atoms has emitted EM radiation

  4. If an electron gains enough energy, it can leave the atom to form an ion

  5. Gamma rays originate from changes in the nucleus of an atom
• Radiation dose: how much exposure leads to harm for a person
• Relationships - EM waves


  As speed is constant for all EM waves - As wavelength decreases, frequency must increase - As frequency increases, energy of the wave increase
• Uses of EM waves

  • Radio - TV and radio o Long wavelength, can travel far without losing quality
  • Micro - Satellite communication, cooking food o Can penetrate atmosphere to reach satellites
  • IR - Cooking food, infrared cameras o Transfers thermal energy
  • Visible - Fibre optics o Best reflection/scattering in glass (others have too short/long wavelengths)
  • UV - Sun tanning, energy efficient lamps o Radiates the least heat but more energy
  • X-ray - Medical imaging and treatment (and gamma) o Very high in energy, and can penetrate material easily