P4 Measuring waves - Use of a ripple tank to measure the speed, frequency and wavelength of a wave

Question 1

Ok what’s a ripple tank

Answer 1

A ripple tank can be used to measure and calculate frequency, wavelength and the speed of waves on the water’s surface. A ripple tank is a transparent shallow tray of water with a light shining down through it onto a white card below to more easily see the motion of the ripples created on the water’s surface. Ripples can be made by hand but to generate regular ripples it is better to use a motor.

Question 2

Aim of the experiment

Answer 2

To measure the frequency, wavelength and speed of waves in a ripple tank.

Question 3

Health and safety

Answer 3

spilled water can be a slip hazard so make sure that spills are dealt with quickly. Make sure any electrical supplies are not close to the water. If class members have photo-induced epilepsy then a stroboscope shouldn’t be used.

Question 4

OCR method 1 - wavelength

Answer 4

1. Set up apparatus as shown below.
2. Use the motor driven beam or a ruler to create a continuous straight wave, this should be of low frequency for easier measuring
3. Use the stroboscope to freeze the wave pattern, if a stroboscope is not available then a digital image of the wave should be taken with the meter ruler lying alongside the wave fronts
4. Find the wavelength by measuring 10 waves on the paper under the ripple tank and finding the average wavelength. If using the camera technique then do the same thing but from the images produced rather than from the paper

Question 5

OCR method 2 - frequency + wave speed

Answer 5

1. Keep the frequency the same as you did for method 1.
2. Use the stop watch and count the number of ripples that pass in a given time, say 10 seconds
   Repeat at least 3 times and calculate a mean
3. Calculate the number of waves that pass per second (frequency)
4. Calculate the wave speed using the equation:
   Wave speed (m/s) = frequency (Hz) x wavelength (m)

Question 6

A student wants to measure the speed of a sound wave using an echo. What apparatus would they need and what measurements should they take? [4 marks]

Answer 6

Equipment needed = stopwatch, meter ruler, wall, person or something to make noise
Place source of noise or person in front of wall, Measure distance to wall from source
Make sound and time how long it takes for echo of sound from wall to be heard
Calculate speed using speed = (2 x distance) x time

Question 7

Equipment

Answer 7

• Ripple tank and accessories (or tray of water if ripple tank not available)
• Motor driven beam with supports to create ripples (or ruler if this is unavailable)
• Hand stroboscope (or digital camera / mobile phone if this isn’t available)
• Metre ruler
• White paper
• Stopwatch

Question 8

Risks/hazards

Answer 8

Electrical components near water Shock and damage to components Secure electrical components before adding water, taking care not to splash

Question 9

Watch a video on this practical

Answer 9

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