 # Wave properties for OCR A-level Physics 1. Wave amplitude
2. Wavelength
3. Wave frequency
4. Wave period
5. Wave speed
6. Phase and phase difference

A wave’s amplitude is a measure of its maximum height from its rest position. The wavelength (λ) of a wave can be shown in a diagram or it can be calculated using the formula: Wavelength = wave speed ÷ frequency. The frequency of a wave is the number of waves that pass a certain point per second. It can be calculated using the waves time period, or speed and wavelength. The time period of a wave is the time it takes a full wave cycle to pass a certain point. It is often calculated using the equation: Time Period = 1 ÷ frequency. Wave speed is the distance travelled by a wave divided by the time it takes. The wave equation can be used to work out the speed of a wave. When talking about phase difference (φ) we can be referring to two separate waves, or two particles in the same wave, and it tells us how far or behind one wave/ particle is from another. Phase difference is measured in radians or degrees and values can range from 0 to 2π or 0 to 360° with the value of π being half a wavelength. In the diagram particles 1 and 3 are in phase, but 1 and 2 are π radian out of phase with each other. # 1

Using the diagram, calculate the speed of the wave shown if it has a wavelength of 25 m.

Speed = Wavelength ÷ Time Period. V = λ ÷ T, V = 25 ÷ 10 = 2.5 m/s. # 2

The vertical displacement of a point on a wave doubles when the amount of energy in the wave doubles. What is the effect on the amplitude of the wave?

It doubles. # 3

State the value of 2 ½ λ in terms of radians and degrees.

2 ½ λ = 2 full wavelengths + ½ a wavelength = 5π rad but this can be simplified to remove complete wavelengths = ½ λ = π rad or 180°. # 4

What is the definition of wavelength?

The wavelength is the distance covered by a full cycle of a wave, this is usually measured as the distance between two peaks or two troughs. # 5

If two particles are half a wavelength apart, what is their phase difference in terms of radians?

1 λ = 2 π, ½ λ = π rad. End of page