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GCSE Questions - Waves

Q14. Here is some apparatus that can be used to investigate the waves in a stretched string.The frequency of the signal generator is adjusted so that a wave is seen - as shown in the diagram. At this frequency the string vibrates between the two positions shown in the diagram.

(a) The wavelength of the wave shown in the diagram was measured as 80 cm. What piece of apparatus would have been suitable for measuring this wavelength?

A metre rule or tape measure

Saying 'ruler' or 'metre stick' did not get you a mark. The ruler is too short and a metre stick does not have 1 cm markings on it.

[1 mark]

(b) Write down the equation which links frequency, wavelength and wave speed.

wave speed = frequency x wavelength

v = fλ

[1 mark]

(c) The string vibrates at 55 Hz. Calculate the wave speed of the wave. Use the data given in the diagram.

80 cm = 0.8 m

v = fλ

v = 55 × 0.8

v = 44 m/s

[3 marks]

(d) The frequency of the signal generator is increased. This makes the wavelength of the wave change. The wave speed stays the same.

Describe how the apparatus could be adjusted to show one complete wave without reducing the frequency.

You could move the (wooden) bridge to the right

OR

You could change the mass/weight on the string by adding more masses/weights (to the string)

[2 marks]

(e) A student wants to investigate how the speed of a wave on a stretched string depends on the tension in the string. The student uses the apparatus in the diagram above.

Describe a method the student could use for this investigation.

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 2:

The design/plan would lead to the production of a valid outcome. All key steps are identified and logically sequenced.

A complete Level 2 answer must include either changing frequency and/or moving the bridge
3 - 4 marks
Level 1:

The design/plan would not lead to a valid outcome. Some relevant steps are identified, but links are not made clear.

But a Level 1 answer must include a way of changing tension

1 - 2 marks
Level 0:

No relevant information
0 marks

 

Indicative content

add or take away masses from the string (ignore any stated values)

adjust frequency using the signal generator and/or move the wooden bridge

observe a steady / stationary pattern to measure the wavelength

calculate wave speed from frequency and wavelength

[4 marks]

(Total 11 marks)