The wave equation in a ripple tank
Change the frequency of the dipper in a ripple tank, measure the wavelength, and discover that frequency × wavelength stays the same.
Core concept
Wave speed = frequency × wavelength (v = f λ); the speed depends on the medium
Topic: Waves
A wave carries energy: What is needed to make things move, heat up, light up or grow. All key words from place to place without carrying the material along. The frequency (f) is how many waves are made each second, in hertz. The wavelength (λ) is the distance from one crest to the next. In one second, f waves each λ long pass a point, so the wave speed: How far something travels in a certain time, like kilometres per hour. All key words is v = f × λ. The speed is set by the medium: in a ripple tank, waves travel more slowly in shallow water. If you make waves faster in the same water, the speed stays the same, so the wavelength gets shorter.
What you will learn
- Measure wavelength and frequency in a ripple tank.
- Use the wave equation v = f × λ.
- Explain why the wavelength changes when the frequency changes but the medium does not.
Before you start
- Know the terms crest, trough, amplitude and wavelength.
Materials
- Water
Equipment
- Ripple tank with a motor-driven dipper, strobe light and ruler
Procedure
- In deep water, set the dipper to 2 Hz, 3 Hz and 6 Hz and record the wavelength each time.
- Work out f × λ for each record.
- Move to shallow water at 3 Hz and compare.
How this simulation is simplified
- Waves travel at 0.30 m/s in the deep part of the tank and 0.15 m/s in the shallow part.