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• A-Level Physics

# Waves

There are two forms of waves - progressive and stationary. Progressive waves transfer energy and can either be transverse, where the vibrations are perpendicular to the direction of travel such as EM waves, or longitudinal, where the vibrations are parallel to the direction of travel such as sound waves. ## Wave Motion

• Displacement, x, is how far the wave has moved from its undisturbed position

• Amplitude, A, is the maximum magnitude of displacement

• Wavelength, λ, is the length of one whole wave cycle, e.g. from peak to peak

• Wave speed, v, is the speed at which the wave moves – the distance it travels per second

• Period, T, is the time taken for the whole cycle to complete

• Frequency, f, is the number of cycles passing a given point per second

• Phase is a measurement of the position of a certain point along the wave

• Phase difference is the amount one wave lags behind another. It is measured in degrees or radians, where one wavelength represents 360° or 2π

### Determining Frequency

Frequency can be determined using a cathode ray oscilloscope to measure voltage. It displays waves from a signal generator as a function of voltage (y-axis) and time (x-axis), from which the time period can be calculated, and this used to work out frequency.

The units of frequency are Hertz, Hz, or /s

The wave equation:

λ = 1/T Frequency = 1 / Time Period

If you know the frequency and the wavelength, you can use the wave equation to work out speed:

v = fλ wave speed = frequency × wavelength

Intensity is the measure of how much energy a wave is carrying. For example, the ‘brightness’ or ‘loudness’ of light and sound waves are just their intensity.

I = P/A Intesnisty = Power / Area

It is proportional to amplitude squared:

Intensity ∝ Amplitude Squared