S-Cool Revision Summary

S-Cool Revision Summary

Types of Waves

Mechanical waves are any waves that move through a medium. For example, water waves.

Progressive waves distribute energy from a point source to a surrounding area. They move energy in the form of vibrating particles or fields.

There are two different types of progressive waves:

- Transverse waves - vibrations are perpendicular to the wave motion - so if the wave is travelling horizontally, the vibrations will be up and down. For example, light and water.

- Longitudinal waves - vibrations are parallel to the wave motion - so if the wave is travelling horizontally, the particles will be compressed closer together horizontally, or expanded horizontally as they go along (we call the expanded bit a rarefaction). The particle movement is a series of compressions and rarefactions. For example, sound and some earthquake waves.

Displacement is the distance a particle moves from its central equilibrium position.

Amplitude is the maximum displacement from the central equilibrium position.

Phase angle is the position along the wave, which is normally measured in degrees or radians. One complete wave is 360 degrees, so from a peak to a trough will be a change in phase of 180 degrees.

Calculating the Speed of a Wave

We can calculate the speed of a wave using:

v = f λ

Where:

v = speed (m/s)

f = frequency (Hz)

λ = wavelength (m)

Standing Waves

Standing waves (also known as stationary waves) are set up as a result of the superposition of two waves with the same amplitude and frequency travelling at the same speed in opposite directions.

The waves are moving, but the position of the crests and troughs are stationary.

Speed of a Wave on a String

We can calculate the speed of a wave using:

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Where:

v = speed (m/s)

F = tension (N)

M = mass per metre of the string (kg/m)

Symbols

Progressive waves

λ = wavelength, m

a = slit spacing in Young's experiment, m

x = fringe separation in Young's experiment, m

D = the distance from the double slit to the screen in Young's experiment, m

d = the slit separation in a diffraction grating, m

n = order number of the fringe (always an integer)

θ = angle from the centre of the diffraction grating to the fringe you are considering (in degrees)