A wave has frequency \(5.0\,\mathrm{Hz}\) and wavelength \(2.4\,\mathrm{m}\). Calculate its speed.
\(v = f\lambda = 5.0\times2.4 = 12\,\mathrm{m\,s}^{-1}\).
Waves
10 exam-style questions on wave properties, speed, reflection, refraction and the electromagnetic spectrum. Tap Show answer for full working.
3 Easy4 Medium3 Hard
State the difference between a transverse wave and a longitudinal wave. Give one example of each.
Transverse: oscillations perpendicular to the direction of energy transfer (e.g. light, water waves, S-waves).
Longitudinal: oscillations parallel to the direction of energy transfer (e.g. sound, P-waves).
List the electromagnetic spectrum in order of increasing frequency, starting with radio waves.
Radio, microwave, infrared, visible, ultraviolet, X-rays, gamma rays.
Sound takes \(0.60\,\mathrm{s}\) to travel \(204\,\mathrm{m}\) in air. Calculate the speed of sound.
\(v = s/t = 204/0.60 = 340\,\mathrm{m\,s}^{-1}\).
A wave has a period of \(0.025\,\mathrm{s}\) and travels at \(12\,\mathrm{m\,s}^{-1}\). Calculate its frequency and wavelength.
\(f = 1/T = 1/0.025 = 40\,\mathrm{Hz}\).
\(\lambda = v/f = 12/40 = 0.30\,\mathrm{m}\).
Describe what happens to the speed, frequency and wavelength of light when it refracts from air into glass.
Speed decreases; frequency stays the same; wavelength decreases (\(\lambda = v/f\)).
Ultrasound of frequency \(2.5\,\mathrm{MHz}\) travels through tissue at \(1500\,\mathrm{m\,s}^{-1}\). Calculate the wavelength. State one medical use of ultrasound.
\(\lambda = v/f = 1500/(2.5\times10^{6}) = 6.0\times10^{-4}\,\mathrm{m}\).
Uses: prenatal scanning, imaging organs, breaking kidney stones.
A student measures the speed of water waves in a ripple tank. 12 crests pass a point in \(4.0\,\mathrm{s}\) and the distance between successive crests is \(3.5\,\mathrm{cm}\). Calculate the wave speed in \(\mathrm{m\,s}^{-1}\).
\(f = 12/4.0 = 3.0\,\mathrm{Hz}\); \(\lambda = 0.035\,\mathrm{m}\).
\(v = f\lambda = 3.0\times0.035 = 0.105\,\mathrm{m\,s}^{-1}\).
Explain why a swimming pool appears shallower than it really is. Use the idea of refraction of light.
Light from the bottom of the pool refracts away from the normal as it leaves the water into air. The rays appear to come from a point higher than the actual bottom, so the pool looks shallower.
Radio waves of wavelength \(3.0\,\mathrm{m}\) are used for communication. Calculate their frequency. (\(c = 3.0\times10^{8}\,\mathrm{m\,s}^{-1}\).) State one advantage of using radio waves for communication.
\(f = c/\lambda = 3.0\times10^{8}/3.0 = 1.0\times10^{8}\,\mathrm{Hz}\) (\(100\,\mathrm{MHz}\)).
Advantages: can travel long distances, pass through atmosphere, not ionising / safe.