Page 2 - WORKSHEET -2 CH 15 CLASS XI

 (c) the frequency of sound as heard by the observer standing on the
platform will increase.
 (d) the frequency of sound as heard by the observer standing on the
platform will decrease.

6 When a source is going away from a stationary observer, with a velocity equal to that of
sound in air, then the frequency heard by the observer will be
(a) Same
(b) Half
(c) Double
(d) One third

7 Ten tuning fork are arranged in increasing order of frequency in such a way that any two
nearest tuning forks produce 4 beats per second. The highest frequency is twice that of the
lowest. Possible highest and lowest frequencies are
(PMT - MP-90, MHT-CET 2002)
(a) 80 & 40
(b) 100 & 50
(c) 44 & 22
(d) 72 & 36

8 Two adjacent piano keys are struck simultaneously. The notes emitted by them have
frequencies n 1 and n 2. the number of beats heard per second is (CPMT-74, 78)

(a)

(b)
(c) (n 1  n 2)
(d) 2 (n 1  n 2)

9 Doppler effect is applicable for (AFMC PUNE-98)
(a) Sound wave
(b) Light waves
(c) None of above
(d) Both ‘a’ and ‘b’

10. A steel rod 100 cm long is clamped at its middle. The fundamental frequency of longitudinal
vibrations of the rod is given to be 2.53 k Hz. What is the speed of sound in steel?

11. A pipe 20 cm long is closed at one end. Which harmonic mode of the pipe is resonantly
excited by a 430 Hz source? Will the same source be in resonance with the pipe if both ends are
-1
open? (speed of sound in air is 340 ms ).