GCSE Physics — Waves — Revision (sample)

Describing waves

A wave transfers energy from one place to another without transferring matter — the water moves up and down, but the wave itself travels along. Waves come in two types, and four measurements describe any of them.

Feature	Transverse	Longitudinal
Vibration direction	perpendicular to the energy transfer	parallel to the energy transfer
Made of	crests and troughs	compressions and rarefactions
Examples	light & all EM waves, water ripples	sound, seismic P-waves

The four measurements

Amplitude

The maximum displacement of a point from its rest position. A bigger amplitude carries more energy.

e.g. A louder sound, or a brighter light, has a larger amplitude.

Wavelength (λ)

The distance between the same point on two adjacent waves — e.g. crest to crest. Measured in metres.

Frequency (f)

The number of complete waves passing a point each second. Measured in hertz (Hz).

Period (T)

The time for one complete wave to pass a point. It is the inverse of frequency: $T = \dfrac{1}{f}$.

A transverse wave: wavelength is crest-to-crest; amplitude is rest-to-crest.

Fill the gaps

A wave transfers tap without transferring tap.

In a tap wave the vibrations are perpendicular to the energy transfer; in a tap wave they are parallel.

Tap each box to check your answer; tap again to hide.

The wave equation

One equation links a wave's speed, frequency and wavelength. It works for every wave, and the exam expects you to rearrange it confidently.

$v = f \times \lambda$

vwave speed (metres per second, m/s)
ffrequency (hertz, Hz)
λwavelength (metres, m)

Rearrange to $f = \dfrac{v}{\lambda}$ to find frequency, or $\lambda = \dfrac{v}{f}$ to find wavelength.

Worked example

A water wave has a frequency of 2 Hz and a wavelength of 1.5 m. Calculate its speed.

1

Write the equation: $v = f \times \lambda$

2

Substitute the values: $v = 2 \times 1.5$

3

Evaluate: $v = 3$

v = 3 m/s

Common error: forgetting the unit (m/s), or mixing up f and λ. Frequency is per second (Hz); wavelength is a distance (m).

3 marks

Calculate the wavelength of a sound wave travelling at 340 m/s with a frequency of 170 Hz.

✓

Rearranges to $\lambda = \dfrac{v}{f}$ (1)

✓

Substitutes: $\lambda = \dfrac{340}{170}$ (1)

✓

$\lambda = 2$ m (correct value and unit) (1)

Calculation questions reward the rearrangement and the unit separately — always show the rearranged formula and write the unit, even if the number is right.

Waves in action

Waves don't just travel in straight lines — they reflect, they refract, and the electromagnetic family forms a whole spectrum, from radio waves to gamma rays.

Reflection

A wave bounces off a surface. The angle of incidence equals the angle of reflection.

e.g. An echo (sound) or your image in a mirror (light).

Refraction

A wave changes direction when it enters a new material and changes speed.

e.g. A straw looks bent where it enters a glass of water.

EM spectrum

All electromagnetic waves are transverse and travel at the same speed in a vacuum, but have different frequencies.

e.g. Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.

The electromagnetic spectrum, in order

Wave	One everyday use
Radio	TV and radio broadcasting
Microwave	cooking; satellite & phone signals
Infrared	remote controls; thermal imaging
Visible light	seeing; fibre-optic communication
Ultraviolet	security marking; sun tanning
X-ray	medical imaging of bones
Gamma	sterilising equipment; treating cancer

Focus

Waves move energy, not matter

A floating duck on a ripple bobs up and down on the spot — it doesn't travel across the pond with the wave. The wave carries energy; the water (the matter) stays put. Examiners love to catch this.

2 marks

Explain what happens to a ray of light when it slows down entering a glass block at an angle.

✓

The light refracts / changes direction (1)

✓

It bends towards the normal (because it slows down) (1)

"Explain" wants the cause: name refraction, then link the change of speed to bending towards the normal.

Self-test

Reading is not revising — answering is. Work through these, and the focus-first round will re-test anything you miss.