Page 2 - WORKSHEET - 1 CH 15 CLASS XI

(d)

7 The wavelength of sound in air is 10 cm. its frequency is, (Given velocity of sound  330
m/s) (CPMT-74)
(a) 330 cycles per second
(b) 3.3 kilo cycles per second
(c) 30 mega-cycles per second
5
(d) 3 × 10 cycles per second

8 When a compression is incident on rigid wall it is reflected as (MHT-CET 2006)
(a) Compression with a phase change of 
(b) Compression with no phase change
(c) Rarefaction with a phase change of 
(d) Rarefaction with no phase change

9 Which of the following statements is wrong
(NCERT-76)
(a) Sound travels in a straight line
(b) Sound travels as waves
(c) Sound is a from of energy
(d) Sound travels faster in vacuum that then in air

10. Earthquakes generate sound waves inside the earth. Unlike a gas, the earth can experience
both transverse (S) and longitudinal (P) sound waves. Typically the speed of S wave is about 4.0
-1
km s . A seismograph records P and S waves from an earthquake. The first P wave arrives 4
min before the first S wave. Assuming the waves travel in straight line, at what distance does
the earthquake.

11. A travelling harmonic wave on a string is described by y (x, t) = 7.5 sin (0.0050x + 12t + π /4)

(a) what are the displacement and velocity of oscillation of a point at x = 1 cm, and t = 1s? Is this
velocity equal to the velocity of wave propagation?
(b) Locate the points of the string which have the same transverse displacement and velocity as
the x = 1 cm point at t = 2s, 5s and 11s.

12. A metre-long tube open at one end, with a movable piston at the other end, shows
resonance with a fixed frequency source (a turning fork of frequency 340 Hz) when the tube
length is 25.5 cm or 79.3 cm. Estimate the speed of sound in air at the temperature of the

experiment. The edge effect may be neglected.