12. (c) The pitch of the sound emitted by the siren of a moving fire engine appears to change as it passes a stationary observer.
(i) Name this phenomenon.
(ii) Explain, with the aid of a diagram, how this phenomenon occurs.
(iii) Will the crew in the fire engine notice this phenomenon? Give a reason for your answer.
(iv) Give an application of this phenomenon. 2011
12. (b) Loudness, pitch and quality are characteristics of a musical note. Name the physical property of a sound wave on which each characteristic depends.
(12)
A bat detector allows us to hear the sounds emitted by bats. The detector is needed as humans cannot hear the sounds emitted by bats as they are outside our frequency limits of audibility.
(i) What is meant by the frequency limits of audibility? (6) (6) (12)
(4) (6)
(ii) What name is given to a sound whose frequency is greater than our upper frequency limit of audibility?
(4)
(iii) A bat emitted a sound wave and detected its reflection from a wall 0.02 s later.
Calculate the distance of the bat from the wall. (speed of sound in air = 340 m s−1) 216 FUSION (6)
