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IGCSE · 3 · multiple choice

Waves · Question 2

Waves · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
routine
Marks
1
Topics
1
Answer
Complete
Profile of the ripple-tank waves at one instant0246810distance / cm2.5 cmone wavelengthdirection of travel
Fig. 2.1A snapshot of the water surface in the ripple tank at one instant, drawn as a side view. Four complete waves run left to right above a horizontal distance scale that is marked in centimetres from 0 to 10, the scale line itself being the undisturbed water level. A dimension line drawn between two neighbouring crests is labelled one wavelength, 2.5 cm, and a separate arrow above the wave shows the direction in which the waves are travelling.
multiple choice1 mark

Water waves in a ripple tank have a wavelength of 2.5 cm. 12 complete waves pass a fixed point in 4.0 s. What is the speed of the waves?

  1. A

    0.83 cm/s

  2. B

    7.5 cm/s

  3. C

    30 cm/s

  4. D

    120 cm/s

Ready to self-mark?Reveal the detailed answer guide
Answer overviewCorrect answer: B — 7.5 cm/s
01

Answer and reasoning

1 mark
How to approach it

Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.

  1. 1

    The correct choice is B: 7.5 cm/s

  2. 2

    C multiplies by the number of waves instead of the frequency — the error of a candidate who never works out that f = 12 / 4.0 = 3.0 Hz.

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