AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Describe a method to measure the speed of ripples on a water surface.
Full specification wording
Properties of waves: describe a method to measure the speed of ripples on a water surface.
To measure the speed of ripples on a water surface, use a ripple tank.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 17 of 18
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
To measure the speed of ripples on a water surface, use a ripple tank. A vibrating bar or dipper touches the water and produces regular ripples. Place a lamp above the tank so the ripples cast shadows on a screen or paper below. Measure the wavelength by recording the distance across several ripple crests and dividing by the number of wavelengths. Measure the frequency from the number of ripples passing a point each second, or read it from the signal generator driving the vibrator. Then calculate speed using speed = frequency × wavelength. For example, if the wavelength is 0.02 m and the frequency is 10 Hz, the speed is 0.2 m/s. This method measures the speed of the water surface waves.
What earns the marks
- Set up a ripple tank with a vibrating bar or dipper producing regular ripples on the water surface.
- Use a lamp above the tank to cast a shadow of the ripples on a screen or paper below, so the ripple pattern can be measured.
- Measure the wavelength by measuring the total distance across several ripple crests and dividing by the number of wavelengths.
- Measure the frequency from the number of ripples passing a fixed point each second, or from the frequency set on the signal generator.
- Calculate the speed of the ripples using speed = frequency × wavelength, and include the unit, for example m/s.
Common mistakes and how to put them right
Measuring the distance between only two adjacent crests, which gives a large percentage error.
Put it right: Measure across several crests and divide by the number of wavelengths.
Confusing frequency with wavelength, for example using the number of ripples in the tank as the frequency.
Put it right: Frequency is the number of ripples passing a point each second, measured in hertz.
Forgetting to convert centimetres to metres before calculating speed.
Put it right: Convert all lengths to metres so the speed is in m/s.
Exam tips
- Describe the ripple tank set-up, including the vibrator, the lamp and the screen used to view the ripple pattern.
- State the equation speed = frequency × wavelength and show the substitution with units.
- Explain how measuring across several wavelengths improves accuracy by reducing the effect of the uncertainty in a single measurement.
Try the lesson
The start of the Properties of waves: describe a method to measure the speed of ripples on a water surface. lesson, made from checked teaching notes for this specification point.
Have a go first
A student uses a ripple tank to make waves on water. Which measurement is needed, together with the distance travelled by a ripple, to calculate the speed of the ripples?
Listen
To measure the speed of ripples on a water surface, use a ripple tank. A vibrating bar or dipper touches the water and produces regular ripples. Place a lamp above the tank so the ripples cast shadows on a screen or paper below. Measure the wavelength by recording the distance across several ripple crests and dividing by the number of wavelengths. Measure the frequency from the number of ripples passing a point each second, or read it from the signal generator driving the vibrator. Then calculate speed using speed = frequency × wavelength. For example, if the wavelength is 0.02 m and the frequency is 10 Hz, the speed is 0.2 m/s. This method measures the speed of the water surface waves. A strong answer earns marks for these points. Set up a ripple tank with a vibrating bar or dipper producing regular ripples on the water surface. Use a lamp above the tank to cast a shadow of the ripples on a screen or paper below, so the ripple pattern can be measured. Measure the wavelength by measuring the total distance across several ripple crests and dividing by the number of wavelengths. Measure the frequency from the number of ripples passing a fixed point each second, or from the frequency set on the signal generator. A common slip: Measuring the distance between only two adjacent crests, which gives a large percentage error. Instead, measure across several crests and divide by the number of wavelengths. Exam tip: Describe the ripple tank set-up, including the vibrator, the lamp and the screen used to view the ripple pattern.
Key words
Say what each word means before you turn the card.
ripple tank
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frequency
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speed = frequency × wavelength
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See every definition
- ripple tank
- A tank used with a vibrating bar or dipper that touches the water and produces regular ripples on the water surface.
- frequency
- The number of ripples passing a point each second, or the value read from the signal generator driving the vibrator.
- speed = frequency × wavelength
- The equation used to calculate the speed of the ripples, with the unit included, for example m/s.
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