Waves
Transverse and longitudinal waves, the wave equation, reflection and refraction, and the electromagnetic spectrum and its uses.
Learn
Waves, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Compare transverse and longitudinal waves
A wave transfers energy without transferring matter. In a transverse wave the oscillations are at right angles to the direction of travel - like ripples on water or light. In a longitudinal wave they are along the direction of travel, as compressions and rarefactions - like sound. Both carry energy, not the material itself.
Describe frequency, wavelength, amplitude and period
Wavelength is the distance for one full wave; amplitude is the maximum displacement from rest, linked to how much energy the wave carries. Frequency is how many waves pass a point each second, in hertz, and the period is the time for one wave. Frequency and period are reciprocals: T = .
Use the wave speed equation
Wave speed links how far and how often: v = fλ, speed equals frequency times wavelength. A wave of frequency 50 Hz and wavelength 6 m travels at 300 m/s. Rearrange to find whichever quantity is missing - the same equation works for sound, water and electromagnetic waves.
Describe reflection and refraction of waves
When a wave meets a boundary it can reflect (bounce back, as an echo or a mirror image) or refract (change direction as it passes into a new material because its speed changes). Light bends towards the normal entering a denser material like glass, which is why a straw looks bent in a glass of water.
Describe the electromagnetic spectrum
Electromagnetic waves are transverse, travel at the speed of light in a vacuum, and form a continuous spectrum by wavelength: radio, microwave, infrared, visible light, ultraviolet, X-ray and gamma. As wavelength shortens the frequency and energy rise, so the order runs from long, low-energy radio waves to short, high-energy gamma rays.
Describe uses and dangers of electromagnetic waves
Each part of the spectrum has its uses: radio for broadcasting, microwaves for cooking and phones, infrared for heating and remote controls, visible light for seeing, and X-rays and gamma for medical imaging and treatment. The higher-energy waves - ultraviolet, X-rays and gamma - can damage cells and cause cancer, so exposure must be controlled.
Waves key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Transverse wave
- A wave whose oscillations are perpendicular to the direction the wave travels, like ripples on water or light.
- Longitudinal wave
- A wave whose oscillations are parallel to the direction the wave travels, with compressions and rarefactions. Sound is longitudinal.
- Amplitude
- The maximum displacement of a point on a wave from its undisturbed (rest) position.
- Wavelength
- The distance from one point on a wave to the same point on the next wave, such as crest to crest. The symbol is λ.
- Frequency
- The number of complete waves passing a point each second, measured in hertz.
- Period
- The time for one complete wave to pass a point: T = .
- Wave speed
- How fast the wave moves through the medium: wave speed = frequency × wavelength (v = fλ).
- Electromagnetic spectrum
- The family of transverse waves from radio waves through microwaves, infrared, visible light, ultraviolet and X-rays to gamma rays, all travelling at the same speed through a vacuum.
Practice
Try a Waves question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
A sound wave has a frequency of 2 kHz and a wavelength of 0.17 m. Work out the speed of the sound, in metres per second (m/s).
- 340
- 3400
- 0.34
- 11800
Show the answer and the working
Answer: 340
First convert: 2 kHz = 2000 Hz. Then v = f × λ = 2000 × 0.17 = 340 m/s.
- Convert the frequency: 2 kHz = 2 × 1000 = 2000 Hz.
- Use the wave equation v = f × λ.
- v = 2000 × 0.17 = 340, so the speed of sound here is 340 m/s.