Waves

Basics

• Waves transfer energy between points, without transferring matter:

  • When a wave travels between two points, no matter actually travels with it: The points on the wave simply vibrate back and forth about fixed positions

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• The wavelength of a wave is the distance from a point on one wave to the same point on the next wave. Usually this is measured from the top of one wave to the top of the next wave

  Wavelength is usually measured in metres (a distance)

• The amplitude of a wave is its height, measured from the middle of the wave to its top (or from the middle to its bottom)

• The frequency of a wave is the number of waves passing a point (or being created or received) every second - it is helpful to think of it as being the waves per second

• The units of frequency are hertz (Hz)

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• Transverse Waves

  • For a transverse wave, the points along the wave vibrate at 90 degrees to the direction in which the wave is moving (the direction of energy transfer)

Longitudinal & Transverse Waves

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• Longitudinal Waves

  • For a longitudinal wave, the points along the wave vibrate in the same direction that the wave is moving in

Longitudinal & Transverse Waves

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Wave equation

• The speed of a wave (v) is related to the frequency (f) and wavelength (λ) by the equation:

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Triangle

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Light from object hits the mirror (i = r)

1. ​To an observer, the reflected ray appears to have come from the right-hand side of the mirror

2. The reflected ray can be traced back in this directions, forming a virtual ray

3. ​This can be repeated for another ray travelling in a slightly different direction

4. An image of the object will appear where these two virtual rays cross

5. The type of image formed in the mirror is called a virtual image

6. A virtual image is formed by the divergence of rays from the image, and cannot be projected onto a piece of paper (because the rays don’t actually go through the image)

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