Transverse and longitudinal waves, the wave terms amplitude, wavelength, frequency and period, and the wave equation v = f lambda.

What this dot point is asking

CCEA wants you to tell the difference between transverse and longitudinal waves, define the wave terms amplitude, wavelength, frequency and period, and use and rearrange the wave equation v = f lambda. Waves transfer energy without transferring matter.

The answer

Transverse and longitudinal waves

In both types, the wave transfers energy in the direction of travel, but the matter (the medium) only vibrates about a fixed position; it is not carried along.

Wave terms

The wave equation

Worked example: a radio wave

Examples in context

Example 1. A slinky spring

Shaking a slinky side to side sends a transverse wave along it; pushing and pulling along its length sends a longitudinal wave with visible compressions and rarefactions, a clear demonstration of both types.

Example 2. Tuning a radio

Changing the station changes the frequency you pick up. Because the wave speed is fixed at $3.0 \times 10^{8}\ \text{m/s}$, a higher frequency means a shorter wavelength, which is why aerials are designed for particular bands.

Example 3. Ripples in a tank

A ripple tank is used in the lab to study waves. A vibrating bar makes straight waves whose frequency you set by the motor; measuring the wavelength on the screen and using $v = f\lambda$ gives the wave speed. Speeding up the motor produces more waves per second (higher frequency) but, at the same speed, a shorter wavelength, showing the inverse link between frequency and wavelength for a fixed speed.

Try this

Q1. State the difference between a transverse and a longitudinal wave. [2 marks]

• Cue. Transverse: vibrations perpendicular to travel; longitudinal: vibrations parallel to travel.

Q2. A wave has a frequency of $20\ \text{Hz}$ and a wavelength of $1.5\ \text{m}$. Find its speed. [2 marks]

• Cue. $v = f\lambda = 20 \times 1.5 = 30\ \text{m/s}$.

Q3. What does the amplitude of a wave tell you? [1 mark]

• Cue. The maximum displacement from rest, linked to the energy the wave carries.