Unit 8: Superposition

• What is the principle of superposition?
• Principle of superposition in the context of waves

  If multiple waves overlap in space and time, the resultant wave will constitute the sum of the amplitudes of the component waves
• What are the two types of interference?
• Two types of interference

  • Constructive
  • Destructive
• What is constructive interference?
• Constructive interference

  When waves superpose such that the amplitude of the wave increases i.e. the maxima of the component waves combine
• What is destructive interference?
• Destructive interference


  When waves superpose such that the amplitude of the wave decreases i.e. maxima and minima of the component waves combine. If this occurs to the maximum extent, oscillations can be nullified completely
• Experiment to investigate the principle of superposition using sound

  Use two speakers, a moderate distance apart, connected to the same signal generator to transmit sound waves. 2. Walk along a line perpendicular to the speakers - you should hear alternating loud and quiet points. 3. This is because in some places the waves from each speaker constructively interfere (loud) and in some places it’s destructive
• What is a stationary wave?
• Stationary waves

  Consist of an alternating fixed pattern of nodes (points with zero amplitude) and antinodes (points with maximum amplitude). No energy is transferred by the wave, it is only stored
• What is a node?
• Node

  A point with no vibrations and at which the resultant amplitude is 0
• What is an antinode?
• Antinode

  A point with maximum vibration and at which the resultant amplitude is at a maximum
• What are the conditions for a stationary wave to be produced?
• Conditions for a stationary wave to be produced

  • The waves must be coherent
  • They must be travelling in opposite directions. These conditions are often met when a wave is reflected back onto itself
• Experiment that demonstrates stationary waves

  Use an oscillator to generate a wave along a string that is fixed at one end. The stationary wave will form when the progressive wave is reflected off the fixed end
• Give a similarity and a difference between stationary waves and progressive waves
• Similarity and difference between stationary waves and progressive waves

  • Similarity: Both have a wavelength, frequency and amplitude. Difference: Stationary waves don’t transmit energy from one place to another
• How to use the formation of stationary waves in a resonance tube to find the speed of sound

  Create a closed end pipe using a hollow pipe inside a measuring
• How could you use the formation of stationary waves in a resonance tube to find the speed of sound?
• Using the formation of stationary waves in a resonance tube to find the speed of sound

  1. Create a closed end pipe using a hollow pipe inside a measuring cylinder containing water

  2. Use a tuning fork (which produces a known frequency) and hold it above the tube

  3. Move the tube up until you find the first position at which resonance occurs

  4. This length will be a quarter of the wavelength

  5. Use speed = frequency x wavelength
• What is meant by ‘harmonics’?
• Harmonics


  Points where the stationary wave form doesn’t change due to the waves in each direction reinforcing each other
• A stationary wave on a string is made to oscillate at its fundamental frequency (1st harmonic) - how many nodes and antinodes would you see?
• How can stationary microwaves be produced experimentally?
• Producing stationary microwaves experimentally

  1. By reflecting a microwave beam

  2. The nodes and antinodes of the reflected wave can be found using a microwave probe
• Identify the nodes and antinodes of these standing waves
• How can the wavelength of a stationary wave be determined?
• Determining the wavelength of a stationary wave

  The wavelength of a stationary wave is equal to twice the distance between adjacent nodes or twice the distance between adjacent antinodes
• Define coherence
• If two waves are in phase will they constructively or destructively interfere?
• True or false? Path difference and phase difference are two names for the same thing
• What is diffraction?
• True or false? Diffraction is most noticeable when the wavelength is much larger than the gap the wave is travelling through
• Describe how a ripple tank might be used to investigate diffraction
• Ripple tank investigation steps

  1. Create water waves in the tank

  2. Vary the size of the gap that they pass through

  3. Note any changes to the direction of the waves passing through
• Why is a laser useful in showing interference and diffraction?
• It produces monochromatic (same wavelength/colour) light