15. Waves
15.1 Progressive waves
15.2 Transverse and longitudinal waves
15.5 Electromagnetic spectrum
15.4 Determination of speed, frequency and wavelength
15.3 Polarisation
5F AS polarisation lab.pdf | |
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Huygens' principle
Huygens' principle states that every point on a wavefront is a source of wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wavefront is a line tangent to all of the wavelets.
Practical- Ripple Tank
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Refraction is the bending of a wavefront resulting from a change in wave speed. This occurs when there is an abrupt change in the medium through which the waves are traveling.
Notice that during the refraction of plane waves across an oblique interface, neither the frequency nor wave shape change. However, the wavelength decreases in the slower medium, the shallow water. This decrease is caused by a reduction in the wave's speed. |
When a wave is refracted upon entering a slower medium, we say that it is "bent towards the normal." Note in the above diagram how the angle of refraction, θr, is smaller than the angle of incidence, θi
Ripple tank interference practical
The central region of constructive interference is known as the central maximum, or Ao. On either side of the central maximum are the first order nodes, N1. These are regions of destructive interference. On either side of N1 are the next antinodes, A1. This alternating pattern of nodes and antinodes continues throughout the construction.
One way to change the amount of interference produced by two in-phase point sources is to change their separation distance but leave their frequency unchanged.
Another way to change the amount of interference produced by two in-phase point sources is to change their frequency but leave their separation distance unchanged.
One way to change the amount of interference produced by two in-phase point sources is to change their separation distance but leave their frequency unchanged.
- When two in-phase point sources are moved closer together, there is less interference produced, as evidenced by fewer nodes. When the amount of interference decreases, the width of any given antinode increases.
- When two in-phase point sources are moved further apart, there is a greater amount of interference produced, as evidenced by a larger number of nodes. When the amount of interference increases, the width of any given antinode decreases.
Another way to change the amount of interference produced by two in-phase point sources is to change their frequency but leave their separation distance unchanged.
- When the frequency is increased, more interference is produced since the wavelengths will decrease, generating more wavefronts between the two sources (the equivalent to moving the point sources further apart).
- When the frequency is decreased, less interference is produced since the wavelengths will increase, generating fewer wavefronts between the two sources (the equivalent to moving the point sources closer together).