properties of waves

• Waves are one way in which energy may be transferred between stores
• Both mechanical and electromagnetic waves will transfer energy but not matter
• Oscillations


  Repeated and regular fluctuations, above and below the same position
• Vibrations


  Repeated movements back and forth (about a fixed point)
• Longitudinal waves


  • Vibrations are parallel to the direction of wave travel
• Transverse waves


  • Vibrations are at right angles to the direction of wave travel
• Mechanical waves


  Cause oscillations of particles in a solid, liquid or gas and must have a medium to travel through
• Electromagnetic waves


  Cause oscillations in electrical and magnetic fields
• All waves transfer energy but they do not transfer matter
• Rest position


  The undisturbed position of particles or fields when they are not vibrating
• Displacement


  The distance that a certain point in the medium has moved from its rest position
• Peak


  The highest point above the rest position
• Trough


  The lowest point below the rest position
• Amplitude


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


  Distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
• Time period


  The time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough
• Frequency


  The number of waves passing a point each second
• Wave period


  The time period of a wave, calculated as 1/frequency
• Calculating wave period


  T = 1/f
• The period (T) is measured in seconds (s), and the frequency (f) is measured in hertz (Hz)
• Calculating wave period


  • For a wave with frequency 50 Hz, the period is 0.02 s
  • For a wave with frequency 400 Hz, the period is 0.0025 s
• Wave speed


  The speed of a wave, calculated as frequency x wavelength
• Calculating wave speed


  v = f x λ
• Wave speed (v) is measured in metres per second (m/s), frequency (f) is measured in Hertz (Hz), and wavelength (λ) is measured in metres (m)
• Calculating wave speed


  • For a wave with frequency 50 Hz and wavelength 6 m, the speed is 300 m/s
  • For a wave with frequency 0.2 Hz and wavelength 25 m, the speed is 5 m/s
• Waves are one way in which energy may be transferred between stores. Both mechanical and electromagnetic waves will transfer energy but not matter.
• The air is made up of many tiny particles. When sound is created, the air particles vibrate and collide with each other, causing the vibrations to pass between air particles. The vibrating particles pass the sound through to a person's ear and vibrate the ear drum.
• Light travels much faster than sound through air.
• Measuring the speed of sound in air

  1. A person fires a starting pistol and raises their hand in the air at the same time

  2. A distant observer 400 metres (m) away records the time between seeing the action (the light reaches the time keeper immediately) and hearing the sound (which takes more time to cover the same distance)

  3. The speed of sound can be calculated using the equation: speed = distance/time
• Speed (v)


  Measured in metres per second (m/s)
• Distance (s)


  Measured in metres (m)
• Time (t)


  Measured in seconds (s)
• Example


  • An observer 400 m away records a 1.2 s time difference between seeing the hand signal and hearing the bang of the starting pistol
  • v = d/t
  • v = 400 ÷ 1.2
  • v = 333 m/s (3 sf)
• The accepted value for the speed of sound in air is 330 m/s.
• The experimental method is flawed as humans do not use stop clocks identically to one another. One person might stop the timer a fraction of a second later than another person. The values recorded will be dependent on the reaction time of the observer, and will not be entirely accurate.
• This explains why the answer of 333 m/s is slightly above the accepted value for the speed of sound in air.
• Waves are one way in which energy may be transferred between stores
• Both mechanical and electromagnetic waves will transfer energy but not matter
• Measuring waves in a ripple tank

  1. Set up the ripple tank

  2. Adjust the height of the wooden rod

  3. Switch on the lamp and motor

  4. Measure the length of a number of waves

  5. Count the number of waves passing a point in ten seconds

  6. Calculate the speed of the waves using: wave speed = frequency × wavelength
• Wavelength


  The length of one wave