Properties of Waves
4 marks · EasyA bell is rung underwater, and the sound travels to a diver who is standing a certain distance away.
State whether sound waves in water are longitudinal or transverse. Explain your answer.
The sound wave in water has a frequency of 800 Hz and a wavelength of 1.9 m. Calculate the speed of sound in water using the wave equation.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Sound waves in water are longitudinal because the vibrations of the water particles are parallel to the direction of energy transfer. · must show mention of vibrations parallel to direction of energy transfer or wave motion
(b) v = 800 × 1.9 = 1520 m/s · must show correct use of v = f × λ, correct substitution and answer
Common mistakes: Omitting explanation of wave type; Calculation using wrong formula
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Marking points
B1 (a) · 1 mark · Correct identification of sound wave as longitudinal.
B2 (a) · 1 mark · Clear explanation: vibrations are parallel to direction of wave or energy transfer.
M1 (b) · 1 mark · Correct substitution into v = f × λ.
A1 (b) · 1 mark · Correct final value with unit: 1520 m/s (accept 1520 with rounding).
Worked solution
a) Sound waves in water are longitudinal because the water particles vibrate backwards and forwards in the same direction as the wave travels, transferring energy without moving water along with the wave.
b) Substitute: f = 800 \text{ Hz}, \lambda = 1.9 \text{ m}