Question
The variation with distance x of the intensity I along a stationary sound wave in air is shown.
The speed of sound in air is 340 m$s^{-1}$.
What is the frequency of the sound wave?
(A) 1700Hz
(B) 2300Hz
(C) 3400Hz
(D) 6800Hz
Answer/Explanation
Ans: C
Question
The diagram shows a string stretched between fixed points X and Y. There is a stationary wave on the string.
The solid curve shows the string at a position of maximum displacement at time t0. The dashed curve shows the other position of maximum displacement. The straight central dashed line shows the mean position of the string. Point S on the string is directly above point P. Point T on the string is directly below point Q.
Which statement is correct?
(A) A short time after $t_{0}$, point R on the string will be displaced.
(B) A short time after $t_{0}$, points S and T on the string move in opposite directions.
(C) The distance between P and Q is one wavelength.
(D) Two moving points on the string that are equal distances from point R vibrate in phase.
Answer/Explanation
Ans: B
Question
The sound from a loudspeaker placed above a tube causes resonance of the air in the tube.
A stationary wave is formed with two nodes and two antinodes, as shown.
The tube has height 60 cm. The speed of sound in the air is $340 m s^{–1}$.
What is the frequency of the sound?
(A) 430Hz
(B) 570Hz
(C) 850Hz
(D) 1700Hz
▶️Answer/Explanation
Ans: A
Question
A stationary wave is formed by two progressive waves travelling in opposite directions along the same line of travel.
Which statement about the two progressive waves is not correct?
(A) They must have a constant phase difference.
(B) They must have the same frequency.
(C) They must have the same wavelength.
(D) They must travel at the same speed.
▶️Answer/Explanation
Ans: A