Starter quiz
- In which of the following directions does the water move in a water wave?
- forwards and backwards
- side to side
- up and down ✓
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- Which of the following accurately describes a water wave?
- longitudinal
- mechanical
- transverse ✓
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- In which of the following directions should a wooden beam move in a trough of water to create water waves?
- up and down ✓
- side to side
- forwards and backwards
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- Which of the following type of results do repeat measurements help to identify?
- accurate results
- anomalous results ✓
- average results
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- A result is ______ if it is very different from other measurements of the same variable.
- 'anomalous' ✓
- Which of the following measurements are needed to find the frequency of a water wave?
- distance and time
- wavelength and time
- wavelength and speed ✓
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Exit quiz
- Which of the following pieces of equipment can be used to observe the behaviour of water waves in the classroom?
- water tank
- ripple tank ✓
- glass trough
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- The frequency of a water wave equals the number of waves ______ second.
- 'per' ✓
- Which of the following happens if the motor controlling the wooden beam on a ripple tank is made to spin faster?
- The frequency of the waves increases. ✓
- The speed of the wave increases.
- The wavelength of the wave increases.
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- The wave speed of a water wave equals the ______ multiplied by the wavelength.
- 'frequency' ✓
- The frequency of a water wave equals the wave speed divided by the ...
- wavelength. ✓
- frequency.
- amplitude.
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- Starting with the most accurate, sort these methods of measuring the wavelength of a water wave into order of decreasing accuracy.
- 1⇔Measure the length of ten waves and divide the answer by ten.
- 2⇔Measure the length of one wave three times and calculate the average.
- 3⇔Measure the length of one wave once.
Worksheet
Presentation
Video
Lesson Details
Key learning points
- Frequency of a wave can be measured indirectly from its speed and wavelength.
- Wavelength of a wave can be measured by using a freeze frame of a wave moving along the length of a ruler.
- It is more accurate to measure the length of, e.g. ten waves and dividing by ten, than measuring one wavelength.
- Speed of a wave can be measured by recording the wave moving along a ruler with a timer in the frame.
- Accurate distance and time are measured by freezing the film, played back in slow motion, to track one wave crest.
Common misconception
In the equation for the speed of a wave, v = f x λ, speed is dependent on frequency and/or wavelength.
Emphasise that the speed of a wave depends only on the wave medium and not on frequency or wavelength.
Keywords
Ripple tank - A vibrating beam in a ripple tank creates water waves in a clear bottomed container that makes the waves easier to observe.
Slow motion - A film played back in slow motion shows everything happening slowly, including the speed of a timer shown in the film.
Wave equation - The wave equation is: wave speed = frequency × wavelength, v = f × λ.
Uncertainty - The uncertainty in a measurement can be expressed as the range of values within which the true value must lie.
Significant figures - The number of significant figures of a measurement depends on how accurately the measurement is made.