waves

• Wave


  A transfer of energy without the transfer of matter
• Wave motion

  • Vibrations in ropes and springs
  • Experiments using water waves
• Wave


  • Wavefront
  • Wavelength
  • Frequency
  • Crest (peak)
  • Trough
  • Amplitude
  • Wave speed
• Wave speed


  v = f λ
• Transverse wave


  Direction of vibration is at right angles to the direction of propagation
• Longitudinal wave


  Direction of vibration is parallel to the direction of propagation
• Wave behaviours

  1. Reflection at a plane surface

  2. Refraction due to a change of speed

  3. Diffraction through a narrow gap
• Ripple tank demonstrations

  1. Reflection at a plane surface

  2. Refraction due to a change in speed caused by a change in depth

  3. Diffraction due to a gap

  4. Diffraction due to an edge
• Diffraction

  • Wavelength and gap size affects diffraction through a gap
  • Wavelength affects diffraction at an edge
• Normal


  A line perpendicular to a surface
• Angle of incidence


  The angle between the incident ray and the normal
• Angle of reflection


  The angle between the reflected ray and the normal
• Reflection by a plane mirror

  1. Formation of an optical image

  2. Characteristics: same size, same distance from mirror, virtual
• For reflection, the angle of incidence is equal to the angle of reflection
• Refraction


  The bending of a wave when it passes from one medium to another
• Refraction experiment

  Refraction of light by transparent blocks of different shapes
• Light passing through a transparent material


  Limited to the boundaries between two media only
• Critical angle


  The angle of incidence for which the angle of refraction is 90°
• Refractive index, n

  The ratio of the speeds of a wave in two different regions
• Refractive index equations


  1. n = sini/sinr

  2. n = 1/sinc
• Optical fibres


  Use in telecommunications
• Thin converging and diverging lenses

  Action on a parallel beam of light
• Focal length


  The distance from the lens to the principal focus
• Principal axis


  The straight line passing through the optical centre of the lens
• Principal focus (focal point)


  The point where parallel rays converge after passing through a converging lens
• Image characteristics

  Enlarged/same size/diminished, upright/inverted, real/virtual
• Magnifying glass


  A single converging lens used to form a virtual, enlarged image
• Corrective lenses


  Converging lenses for long-sightedness, diverging lenses for short-sightedness
• Dispersion of light by a glass prism

  Refraction of white light
• Visible spectrum colours


  • In order of frequency and wavelength
• Monochromatic light


  Light of a single frequency
• Regions of the electromagnetic spectrum

  • In order of frequency and wavelength
• All electromagnetic waves travel at the same high speed in a vacuum
• Uses of electromagnetic spectrum regions

  • Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays
• Excessive exposure to electromagnetic radiation can have harmful effects on people
• Microwaves


  Internal heating of body cells
• Infrared


  Skin burns
• Ultraviolet


  Damage to surface cells and eyes, leading to skin cancer and eye conditions
• 1. rays and gamma rays

  Mutation or damage to cells in the body
• Communication with artificial satellites

  1. Mainly by microwaves

  2. Some satellite phones use low orbit artificial satellites

  3. Some satellite phones and direct broadcast satellite television use geostationary satellites