Edexcel GCSE Physics Topic 4: Waves Exam Questions

About Edexcel GCSE Physics Topic 4: Waves

Topic 4 on Paper 1 introduces the properties of waves and how they transfer energy and information without transferring matter. You need to describe transverse and longitudinal waves, use v = f x lambda and v = x / t, and explain what happens at boundaries through reflection, refraction, transmission and absorption. The separate physics content extends this to how the ear detects sound, ultrasound for sonar and medical scanning, infrasound, and how P and S waves reveal the Earth's interior structure. It leads directly into Topic 5 on light and the electromagnetic spectrum. The core practical on measuring wave speed in water and in solids is frequently examined.

What you need to know

• Wave types Transverse waves oscillate at right angles to the direction of energy transfer (water ripples, light). Longitudinal waves oscillate parallel to it, with compressions and rarefactions (sound, seismic P waves).
• Wave terms Amplitude, wavelength, frequency and period. Frequency is the number of waves per second in hertz, and period T = 1 / f.
• Wave equations Wave speed = frequency x wavelength (v = f x lambda) and wave speed = distance / time (v = x / t).
• Refraction Waves change speed when they enter a different medium, which can change their direction. They bend towards the normal when they slow down.
• Sound and the ear Sound travels faster in solids than in gases. In the ear, sound waves make the eardrum vibrate; humans hear roughly 20 Hz to 20 000 Hz.
• Ultrasound and infrasound Ultrasound is above 20 000 Hz and is used in sonar and foetal scanning by timing echoes. Infrasound is below 20 Hz and is used to detect events such as volcanic eruptions and animal communication.
• Seismic waves P waves are longitudinal and travel through solids and liquids. S waves are transverse and cannot travel through liquids, which is evidence for the Earth's liquid outer core.
• Core practical Measure wave speed in a ripple tank using frequency and wavelength, and measure the speed of sound in a solid rod using frequency from a struck rod.

Common mistakes in Topic 4: Waves

• Saying waves transfer matter. Waves transfer energy and information; the particles of the medium only oscillate about fixed positions.
• Forgetting to halve the total distance in echo calculations. The pulse travels to the object and back.
• Saying the frequency changes during refraction. The frequency stays the same; the speed and wavelength change.
• Describing longitudinal waves as having peaks and troughs. They have compressions and rarefactions.
• Stating that S waves travel through the outer core. S waves cannot travel through liquids, which creates the S wave shadow zone.

Try three Topic 4: Waves exam-style questions