6. Waves

• Waves transfer energy from one place to another without transferring matter
• Transverse waves


  Waves where the oscillations are perpendicular to the direction of energy transfer
• Transverse waves


  • Crest (peak)
  • Trough
  • Displacement
  • Amplitude
  • Wavelength
• Examples of transverse waves


  • Electromagnetic waves (like visible light)
  • Water waves
  • Seismic waves (S-waves)
• Longitudinal waves


  Waves where the oscillations are parallel to the direction of energy transfer
• Longitudinal waves


  • Compression
  • Rarefaction
  • Wavelength
• Examples of longitudinal waves


  • Sound waves
  • Seismic waves (P-waves)
• Frequency


  The number of waves that pass a certain point in one second
• Period


  The time it takes for one complete wave to pass a point
• Measuring the speed of sound (direct measurement)


  1. Two people stand 100 meters apart

  2. One person claps two bricks

  3. The other person uses a stopwatch to time from when they see the clap to when they hear the sound

  4. Repeat and find the average time

  5. Use the formula to calculate the speed of sound
• Measuring the speed of sound (echoes)


  1. Two people stand 50 meters from a wall

  2. One person claps two bricks

  3. The other person uses a stopwatch to time from when they see the clap to when they hear the echo

  4. Repeat and find the average time

  5. Use the formula to calculate the speed of sound, doubling the distance to account for the echo
• Measuring the properties of water ripples


  1. Use a ripple tank

  2. Measure frequency by timing waves passing a fixed point

  3. Measure wavelength by photographing waves and measuring distance between wavefronts

  4. Measure speed by timing how long it takes a wavefront to travel a measured distance
• Measuring the properties of waves on a string

  1. Use a signal generator to vibrate the string

  2. Adjust the frequency to get a clear wave pattern

  3. Measure the wavelength by measuring multiple wavelengths and dividing by the number

  4. The frequency is the setting on the signal generator

  5. Calculate the speed using the wave equation
• Electromagnetic waves are transverse waves that can travel through a vacuum
• Types of electromagnetic waves


  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• Visible light


  The part of the electromagnetic spectrum that can be detected by the human eye, appearing as different colours
• Refraction


  When a wave encounters a boundary between two materials, it can be absorbed, reflected, or transmitted and change speed and direction
• When a wave travels from a less dense medium to a more dense medium, its speed and wavelength decrease but its frequency stays the same
• When a wave travels from a more dense medium to a less dense medium, its speed and wavelength increase but its frequency stays the same
• Wavefront diagram


  A diagram where each line represents the peak of a wave, and the distance between the lines is the wavelength
• When a wave enters a new medium at an angle


  The wave bends towards the normal (a line perpendicular to the surface) if going from a less dense to a more dense medium
• Frequency


  Stays the same
• Wave travels from a more dense medium to a less dense medium


  Speed and wavelength increases, frequency stays the same
• Light waves travelling through


  • Air (less dense)
  • Glass (more dense)
• Light entering perpendicularly


  It does not bend - it just passes straight through
• Wavefront diagram


  Each line represents the peak of a wave, distance between lines is the wavelength
• Wave enters new medium at an angle


  Direction of the wave changes
• Wave travels from less dense to more dense medium


  Wave bends towards the normal
• Wave travels from more dense to less dense medium


  Wave bends away from the normal
• Radio waves


  Used in wireless communication such as TV and radio
• How radio waves are transmitted and received


  1. In transmitting antenna: Electrons move up and down creating radio waves that radiate away

  2. In receiving antenna: Metal aerial absorbs incoming radio waves, causing electrons to vibrate and create alternating current
• Microwaves


  • Ideal for satellite communications, can penetrate Earth's atmosphere with little interference
  • Used in cooking to excite water molecules and heat food quickly and efficiently
• Infrared


  • Used in electrical heaters to directly warm objects and people
  • Used in infrared cameras to detect heat, useful in night-vision devices
• Visible light


  • Used in fibre optic communications to carry large amounts of data over long distances with little signal loss
• Ultraviolet


  • Used in energy-efficient lamps where UV light is converted into visible light
  • Used in tanning beds
• 1. rays and gamma rays


  • Critical in medical imaging such as X-ray radiography
  • Gamma rays used in cancer treatment to target and destroy cancer cells
• Atomic and nuclear changes


  1. Electron absorbs electromagnetic radiation and moves to higher energy level

  2. Electron emits electromagnetic radiation and moves to lower energy level
• Sievert (Sv)


  Unit that assesses the risk of harm from radiation exposure
• Ultraviolet rays


  • Can cause skin to age prematurely and increase risk of skin cancer due to ability to damage genetic material in skin cells
• 1. rays and gamma rays


  • Ionising radiation that can remove tightly bound electrons from atoms, causing cellular and DNA damage and increasing cancer risk