- 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