Question
A vehicle moves with constant velocity along a road directly towards an observer. The observed frequency of the sound from the vehicle changes as the vehicle moves past the observer.
Which phenomenon explains the change in frequency?
(A) diffraction
(B) interference
(C) polarisation
(D) the Doppler effect
Answer/Explanation
Ans: D
Question
A source X emits a sound wave of constant frequency f. The wave is subsequently received at a stationary detector Y. The frequency of the wave that is detected by Y is less than f.
What could be the reason for this?
(A) Between X and Y, the wave undergoes diffraction.
(B) Between X and Y, the wave undergoes reflection.
(C) X is moving away from Y.
(D) X is moving towards Y.
▶️Answer/Explanation
Ans: C
Question
A car travels at a constant speed along a straight line PQ.
A loudspeaker attached to the car emits sound of constant frequency f. A stationary observer is at point O.
What does the observer hear as the car moves from P towards Q?
(A) a frequency less than f that decreases as the car moves from P towards Q
(B) a frequency less than f that increases as the car moves from P towards Q
(C) a frequency more than f that decreases as the car moves from P towards Q
(D) a frequency more than f that increases as the car moves from P towards Q
▶️Answer/Explanation
Ans: C
Question
The range of frequencies of sound waves emitted by blue whales is 10Hz to 40 Hz. The speed of sound in seawater is approximately 1.5 \(km s^{–1}\). What is the approximate range of wavelengths of the sound waves emitted by blue whales?
A 6.7 mm to 27 mm
B 3.8 cm to 15 cm
C 6.7 m to 27 m
D 38 m to 150 m
▶️Answer/Explanation
Ans D