Topic 4

• Waves


  Transfer energy and information but do not transfer matter
• Types of waves


  • Transverse
  • Longitudinal
• Transverse wave


  A wave for which the oscillations are perpendicular to the direction of energy transfer
• Longitudinal wave


  A wave for which the oscillations are parallel to the direction of energy transfer
• Transverse waves


  • EM waves
  • Seismic s-waves
• Longitudinal waves


  • Sound waves
  • Seismic p-waves
• Parts of a longitudinal wave

  Compressions and rarefactions
• Parts of a transverse wave

  Peaks and troughs
• Amplitude


  The maximum displacement of a point on a wave from its undisturbed position
• Wavelength


  The distance from a point on a wave to the same position on the adjacent wave, most commonly peak to peak or trough to trough
• Frequency


  The number of waves that pass a given point each second
• Unit of frequency


  Hertz, Hz
• Frequency of 200Hz


  200 waves pass a given point each second
• Wave speed


  The speed at which energy is transferred through a medium
• Waves transfer energy
• Wave velocity


  Wave velocity (measured in metres per second) is equal to the product of the wavelength and frequency of the wave
• Calculating wave speed


  1. Wave Speed = Frequency x Wavelength

  2. Speed (m/s), Frequency (Hz), Wavelength (m)
• Period of a wave

  The length of time it takes for one full wave to pass through a point
• concave is diverging
• convex is converging
• convex produces real and virtual
• convex is wider in the middle
• A real image appears on the other side of the lens to the object. We can project real images onto a screen.
• A real image appears on the other side of the lens to the object. We can project real images onto a screen.
• Concave lenses only produce virtual images.
• Virtual images are always upright because they cannot be projected onto a screen.
• When light rays pass through a convex lens, they bend towards the normal line at every point.
• Light bends away from the normal when it passes through a concave lens.
• The frequency of the wave does not change because the source is producing the same number of oscillations (vibrations) per second
• Frequency is measured over time.
• The amplitude of the wave changes as the energy transferred by the wave increases or decreases.
• Amplitude is the maximum displacement of an object from its equilibrium position.
• Speed is the rate at which waves travel.
• When light falls on a matt black surface, most of the energy is absorbed.
• • If light slows down as it enters a new medium, this medium is “more optically dense”.
  • When light enters a more optically dense medium, it is refracted closer to the normal.
  • This means that the angle of refraction is smaller than the angle of incidence.
• • If light speeds up on entering a new medium, this medium is “less optically dense”.
  • The light is refracted further from the normal - the angle of refraction is larger than the angle of incidence.
• The angle of refraction is the angle between the refracted light ray and the normal. When light enters a more optically dense medium, it is refracted closer to the normal and the angle of refraction is smaller.
• The angle of refraction is the angle between the refracted light ray and the normal. When light enters a more optically dense medium, it is refracted closer to the normal and the angle of refraction is smaller.
• If the angle of incidence (i) is greater than the critical angle:

  No refraction occurs. All the light is reflected (not refracted) back into the denser medium.

  This is total internal reflection.
• Criteria for TIR

  1. The rays of light must travel from a more dense medium to a less dense medium (e.g. from glass to air).
  2. The angle of incidence must be greater than the critical angle.