3. Waves

• Waves


  A transfer of energy, not the transfer of matter (Can be seen as a transfer of information such as sound waves)
• Period


  How long it takes for a wave to pass/travel
• Wavelength (λ)


  Unit: m
• Wave speed (V)


  Unit: m/s
• Frequency (F)


  Unit: Hz (Hertz)
• MHz


  1,000,000 Hz (10^6)
• Wave types


  • Transverse
  • Longitudinal
• Transverse waves


  • Vibrations travel perpendicular to the direction of the wave
• Longitudinal waves


  • Vibrations travel parallel to the direction of the wave
• Crest


  Top of a transverse wave
• Trough


  Bottom of a transverse wave
• Amplitude


  Measured from the baseline to either the crest or trough
• Wavelength


  Measured from one point to another identical point in the wave (crest to crest or trough to trough)
• Compression


  Section where a longitudinal wave is close together
• Rarefaction


  Section where a longitudinal wave is far apart
• Frequency (f)


  How many waves are passing per second. One hertz = One wave a second
• Doppler effect


  An apparent change in frequency is perceived when relative motion exists between the wave source and the receiver
• As the sound wave source moves closer


  The frequency increases and becomes a higher frequency/pitch
• As the sound wave source moves away


  The frequency decreases and the sound becomes a lower frequency/pitch
• Light, a higher frequency/low wavelength

  The object will seem purple/blue
• For light, a lower frequency/high wavelength


  The object will seem more red
• Electromagnetic waves


  • Radio waves
  • Microwaves
  • Infrared radiation
  • Visible light
  • Ultraviolet
  • Gamma radiation
• Radio waves


  Used mainly for communication
• Microwaves


  Used for satellite communication and heating food
• Infrared radiation


  Used for heating and to monitor temperature
• Visible light


  Used for photography
• Ultraviolet


  Used in fluorescent lamps
• Gamma radiation


  Can be very useful for sterilising medical equipment and sterilising food
• Radio Waves

  Have the lowest frequency
• Infrared


  Can cause a heating effect by making surface molecules vibrate. Too much exposure can cause skin burns
• Ultraviolet


  Can damage surface cells and cause blindness
• Gamma rays


  Have the highest frequency which can cause cell mutation and tissue damage
• Light can exhibit


  • Ray (e.g. reflection)
  • Wave (e.g. interference and diffraction)
  • Particle (e.g. photoelectric effect)
• According to the concept of wave-particle duality in quantum mechanics, light exhibits both particle and wave nature, depending upon the circumstances
• What can happen when light travels from one medium to another


  • Gets absorbed (absorption)
  • Bounces back (reflection)
  • Passes through or bends (refraction)
• When light is incident on a plane mirror, most of it gets reflected, and some of it gets absorbed in the medium
• The speed of light is a constant which is 2.998×10^8 m/s or approximately 3.0×10^8 m/s
• A medium that is polished well without any irregularities on its surface will cause regular reflection of light. For example, a plane mirror. But even then, some light gets absorbed by the surface
• The incident ray, reflected ray and the normal all lie in the same plane. Angle of incidence = Angle of reflection [∠i=∠r]
• Waves have a frequency higher than the upper limit for human hearing – above 20,000 Hertz (Hz). Different species of animals have different hearing ranges. This explains why a dog can hear the ultrasound produced by a dog whistle, but humans cannot