# NCERT Physics Class 11 Exemplar Ch 15 Waves Part 2

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## MCQ II

11. A transverse harmonic wave on a string is described by

Where x and y are in cm and t is in s. The positive direction of x is from left to right.

(a) The wave is travelling from right to left.

(b) The speed of the wave is 20m/s.

(c) Frequency of the wave is 5.7 Hz.

(d) The least distance between two successive crests in the wave is 2.5 cm.

Ans: (a), (b), (c)

12. The displacement of a string is given by where x and y are in m and t in s. The length of the string is 1.5m and its mass is .

(a) It represents a progressive wave of frequency 60Hz.

(b) It represents a stationary wave of frequency 60Hz.

(c) It is the result of superposition of two waves of wavelength 3 m, frequency 60Hz each travelling with a speed of 180 m/s in opposite direction.

(d) Amplitude of this wave is constant.

Ans: (b), (c)

13. Speed of sound waves in a fluid depends upon

(a) Directly on density of the medium.

(b) square of Bulk modulus of the medium.

(c) Inversely on the square root of density.

(d) Directly on the square root of bulk modulus of the medium.

Ans: (c), (d)

14. During propagation of a plane progressive mechanical wave

(a) All the particles are vibrating in the same phase.

(b) Amplitude of all the particles is equal.

(c) Particles of the medium executes S.H.M.

(d) Wave velocity depends upon the nature of the medium.

Ans: (b), (c), (d)

15. The transverse displacement of a string (clamped at its both ends) is given by.

All the points on the string between two consecutive nodes vibrate with

(a) Same frequency

(b) Same phase

(c) Same energy

(d) Different amplitude.

Ans: (a), (b), (d)

16. A train, standing in a station yard, blows a whistle of frequency 400 Hz in still air. The wind starts blowing in the direction from the yard to the station with a speed of 10m/s. Given that the speed of sound in still air is 340m/s,

(a) The frequency of sound as heard by an observer standing on the platform is 400Hz.

(b) The speed of sound for the observer standing on the platform is 350m/s.

(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.

Ans: (a), (b)

17. Which of the following statements are true for a stationary wave?

(a) Every particle has a fixed amplitude which is different from the amplitude of its nearest particle.

(b) All the particles cross their mean position at the same time.

(c) All the particles are oscillating with same amplitude.

(d) There is no net transfer of energy across any plane.

(e) There are some particles which are always at rest.

Ans: (a), (b), (d), (e)