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 Double Award 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, and the wave-equation calculation appears in most P2 papers.

Transverse and longitudinal waves

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

Wave terms

The wave equation

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 studies waves in the lab. A vibrating bar makes straight waves whose frequency you set; measuring the wavelength on the screen and using $v = f\lambda$ gives the wave 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.