Wave Properties and Behaviour
Waves are regular oscillations that transfer energy, and sometimes information, from one place to another without transferring matter itself, since the particles or fields that make up the wave oscillate about a fixed position rather than travelling with it. GCSE physics splits waves into transverse waves, such as light, which oscillate at right angles to the direction of travel, and longitudinal waves, such as sound, which oscillate parallel to it, forming compressions and rarefactions.
Before you start
No specific prerequisites - this is a good place to start.
Method
- Identify whether the wave described is transverse (oscillation perpendicular to travel, e.g. light, water) or longitudinal (oscillation parallel to travel, with compressions and rarefactions, e.g. sound), since some questions simply test this classification.
- Learn the definitions precisely: amplitude is the maximum displacement of a point on the wave from its undisturbed (rest) position, measured from the centre line, not peak to trough; wavelength (lambda) is the distance from one point on a wave to the equivalent point on the next wave (e.g. crest to crest), in metres; frequency (f) is the number of complete waves passing a fixed point per second, in hertz (Hz); period (T) is the time for one complete wave/oscillation, in seconds.
- Use the two equations that connect these quantities: period T = 1 / f, and wave speed v = f x wavelength. Rearrange using the triangle method when the question asks for f or wavelength instead of v.
- Remember energy transfer happens without matter transfer: a cork bobbing on a water wave moves up and down but does not travel across the pond with the wave, and a stationary air particle vibrates back and forth as a sound wave passes but does not travel from source to ear.
- For reflection questions, apply angle of incidence = angle of reflection, both measured from the normal (an imaginary line at right angles to the surface).
- For refraction questions, explain the bend in terms of a change in wave speed at the boundary: frequency stays constant (it is set by the source), so if speed decreases, wavelength must decrease too (from v = f x wavelength), and the wave bends towards the normal; if speed increases, wavelength increases and the wave bends away from the normal.
- For the required practical on waves, be ready to describe the apparatus, identify the independent, dependent and control variables, and explain how to reduce the percentage uncertainty in a wavelength measurement.
Worked example
A student uses a signal generator and a vibration transducer to send waves along a stretched string. The signal generator is set to a frequency of 25 Hz. The student measures the distance covered by 5 complete waves on the string as 100 cm. Calculate the speed of the wave on the string.
- Find the wavelength: 5 complete waves span 100 cm, so one wavelength = 100 / 5 = 20 cm.
- Convert to metres: 20 cm = 0.20 m (divide by 100).
- Write the wave equation: wave speed = frequency x wavelength (v = f x wavelength).
- Substitute: v = 25 x 0.20.
- Calculate: 25 x 0.20 = 5.0.
- Final answer: the wave speed is 5.0 m/s. Measuring across 5 waves rather than 1 reduces the percentage uncertainty in the wavelength measurement, since the same ruler-reading error is now spread over a much larger distance.
Practice questions
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Q1State the difference between a transverse wave and a longitudinal wave.Show answer
Answer: In a transverse wave the oscillations are at right angles (perpendicular) to the direction of energy transfer (e.g. light); in a longitudinal wave the oscillations are parallel to the direction of energy transfer, forming compressions and rarefactions (e.g. sound).
Q2A wave has a frequency of 50 Hz. Calculate its period.Show answer
Answer: 0.02 s (T = 1/f = 1/50 = 0.02 s)
Q3A water wave has a wavelength of 0.4 m and a frequency of 2.5 Hz. Calculate its speed.Show answer
Answer: 1.0 m/s (v = f x wavelength = 2.5 x 0.4 = 1.0 m/s)
Q4Sound waves travel through a steel rail at approximately 5900 m/s. A sound wave sent along the rail has a frequency of 2950 Hz. Calculate its wavelength.Show answer
Answer: 2.0 m (wavelength = v/f = 5900/2950 = 2.0 m)
Q5Explain, in terms of particle motion, why a wave can transfer energy without transferring matter.Show answer
Answer: The particles of the medium oscillate about a fixed position and return to it each cycle; they do not travel along with the wave, so only energy, not matter, moves from source to receiver.
Q6A wave travels from air into glass and slows down. State what happens to its direction, and explain why in terms of wavelength.Show answer
Answer: It bends towards the normal; because the frequency is unchanged but the speed decreases, the wave equation v = f x wavelength means the wavelength must also decrease.
Q7Give one everyday example of a transverse wave and one everyday example of a longitudinal wave.Show answer
Answer: Transverse: light, or a ripple on water. Longitudinal: sound, or a P-wave (primary seismic wave).
Q8A wave has a period of 0.005 s. Calculate its frequency.Show answer
Answer: 200 Hz (f = 1/T = 1/0.005 = 200 Hz)
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
A student carries out the required practical to determine the speed of water waves in a ripple tank. The dipper produces 8 complete waves every 4.0 seconds, and the distance from the first wave crest to the ninth wave crest is measured as 72 cm. (a) Calculate the frequency of the waves. (b) Calculate the wavelength of the waves, in metres. (c) Calculate the speed of the waves.
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A student is asked to plan an experiment using a ripple tank to determine the speed of water waves. Describe a method the student could use, including how to measure the wavelength and frequency, and explain one way to reduce the percentage uncertainty in the measurements.
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Sound waves travel through air at approximately 340 m/s. Calculate the wavelength of a sound wave of frequency 400 Hz travelling through air. Give your answer to 2 significant figures.
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Free printable worksheet
Want more practice on paper? Download the wave properties and behaviour worksheet pack - 11 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 18 of GCSE Physics Workbook, the whole course as one free printable PDF.
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