# 3.1.1 Waves

### Waves: Basics

• Waves transfer energy between points, without transferring matter:
• When a wave travels between two points, no matter actually travels with it: The points on the wave simply vibrate back and forth about fixed positions
• The wavelength of a wave is the distance from a point on one wave to the same point on the next wave. Usually this is measured from the top of one wave to the top of the next wave
Wavelength is usually measured in metres (a distance)
• The amplitude of a wave is its height, measured from the middle of the wave to its top (or from the middle to its bottom)
• Wavefronts are a useful way of picturing waves from above: each wavefront is used to represent a single wave Diagram showing a wave drawn as a series of wavefronts

• The frequency of a wave is the number of waves passing a point (or being created or received) every second – it is helpful to think of it as being the waves per second
• The units of frequency are hertz (Hz)

#### Exam Tip

When labelling wavelength on a diagram, make sure that your arrows go from the very top of a wave to the very top of the next one: if your arrow is too short you will lose marks.

### Longitudinal & Transverse Waves

• Waves can exist as one of two main types:
• Transverse
• Longitudinal

Transverse Waves

• For a transverse wave, the points along the wave vibrate at 90 degrees to the direction in which the wave is moving (the direction of energy transfer) With a transverse wave, the vibrations are at 90 degrees to the direction of energy transfer

Longitudinal Waves

• For a longitudinal wave, the points along the wave vibrate in the same direction that the wave is moving in With a longitudinal wave, the vibrations are parallel to the direction of energy transfer

#### Exam Tip

If asked to describe the difference between transverse and longitudinal waves, sketch the above diagrams. A good, clearly labelled diagram can earn you full marks.

Extended Only

### The Wave Equation

• You can rearrange this equation with the help of the formula triangle: #### Exam Tip

When stating equations make sure you use the right letters:
Eg. λ for wavelength, not L or W.

If you can’t remember the correct letters, then just state the word equations.

Be careful with units: wavelength is usually measured in metres and speed in m/s, but if the wavelength is given in cm you might have to give the speed in cm/s.

Likewise, watch out for frequency given in kHz: 1 kHz = 1000 Hz ### Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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