Properties of Waves
4 marks · NormalA percussionist strikes a drum repeatedly at a constant rate, producing sound waves.
State whether sound waves in air are longitudinal or transverse and explain your answer.
The time between drum beats is . Calculate the frequency of the sound waves produced by the drum.
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.
Show answer
(a) Sound waves in air are longitudinal because the vibrations of air particles are parallel to the direction of energy transfer. · must show longitudinal definition, relation to sound
(b) 20 Hz · must show use of f=1/T, correct substitution
Common mistakes: Saying sound in air is transverse; Incorrectly inverting period to get frequency
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies sound waves as longitudinal.
B2 (a) · 1 mark · Gives correct explanation relating vibration direction to energy transfer.
M1 (b) · 1 mark · Writes or uses formula, or substitutes values.
A1 (b) · 1 mark · Correct frequency (20 Hz). (follow-through)
Worked solution
a) Sound waves in air are longitudinal because the air particles vibrate in the same direction as the wave is travelling.
b)