Waves, Light, and Sound
Key definitions, formulas, and behaviours of waves for beginner physics exams.
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Questions Covered in This Set
12 cards to master
What is a wave?
A disturbance that transfers energy from one place to another without transferring matter.
Transverse wave
Oscillation is at right angles (90°) to the direction of travel — e.g. light, water ripples, S-waves. Can be polarised.
Longitudinal wave
Oscillation is parallel to the direction of travel, creating compressions and rarefactions — e.g. sound, P-waves.
State the wave equation and units
v = fλ; speed in m/s, frequency in Hz, wavelength in m.
Relationship between period and frequency
T = 1/f (period in seconds, frequency in hertz).
Law of reflection
Angle of incidence = angle of reflection, both measured from the normal (line at 90° to the surface).
What happens when light enters a denser medium (air → glass)?
It slows down and bends towards the normal; wavelength decreases but frequency stays the same.
Why is there no sound in space, but we still see starlight?
Sound is longitudinal and needs a medium to travel through; light is electromagnetic and travels through a vacuum at 3 × 10⁸ m/s.
A sound wave travels at 340 m/s with frequency 170 Hz. Find λ.
λ = v/f = 340/170 = 2 m.
An echo returns from a cliff in 2.0 s (speed 340 m/s). How far is the cliff?
Distance travelled = 340 × 2.0 = 680 m; halve it because sound went there and back, so cliff is 340 m away.
Order of the EM spectrum (increasing frequency)
Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays.
Total internal reflection
When light hits a boundary into a less dense medium beyond the critical angle, none escapes and all is reflected — used in optical fibres.
