CBSE - Physics - Sound

1. Note is a sound
(a) of mixture of several frequencies
(b) of mixture of two frequencies only
(c) of a single frequency
(d) always unpleasant to listen
Ans. (a) of mixture of several frequencies
Explanation: Note is a sound of mixture of several frequencies and is pleasant of hear.

2. A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case
(a) sound will be louder but pitch will not be different
(b) sound will be louder and pitch will also be higher
(c) sound will be louder but pitch will be lower
(d) both loudness and pitch will remain unaffected
Ans. (a) sound will be louder but pitch will not be different
Explanation: The pitch depends on frequency of the particular key which is being hit and hence there would be no change in pitch of sound. Loudness depends on amplitude which will be more if key is struck harder.

3. In SONAR, we use
(a) ultrasonic waves
(b) infrasonic waves
(c) radio waves
(d) audible sound waves
Ans. (a) ultrasonic waves

4. Sound travels in air if
(a) particles of medium travel from one place to another
(b) there is no moisture in the atmosphere
(c) disturbance moves
(d) both particles as well as disturbance travel from one place to another.
Ans. (c) disturbance moves
Explanation: Propagation of sound does not require movement of particles. It only requires movement of disturbance from one particles to the next.

5. When we change feeble sound to loud sound we increase its
(a) frequency
(b) amplitude
(c) velocity
(d) wavelength
Ans. (b) amplitude
Explanation: Loudness of sound depends on amplitude and it increases when amplitude is increased.

6. In the curve (Fig.12.1) half the wavelength is

(a) AB
(b) BD
(c) DE
(d) AE
Ans. (b) BD
Explanation: The distance between two consecutive peaks or two consecutive troughs is called wavelength. The figure shows one peak and one trough. Sum of widths of a peak and trough is also same as wavelength; which is AE in this case. Hence, BD is half the wavelength.

7. Earthquake produces which kind of sound before the main shock wave begins
(a) ultrasound
(b) infrasound
(c) audible sound
(d) none of the above
Ans. (b) infrasound
Explanation: It is due to infrasound that some animals get advanced warning of earthquake and show strange changes in their behaviour.

8. Infrasound can be heard by
(a) dog
(b) bat
(c) rhinoceros
(d) human beings
Ans. (c) rhinoceros
Explanation: Rhinoceros communicate using infrasound of as low frequency as 5 Hz.

9. Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting
(a) intensity of sound only
(b) amplitude of sound only
(c) frequency of the sitar string with the frequency of other musical instruments
(d) loudness of sound
Ans. (c) frequency of the sitar string with the frequency of other musical instruments Explanation: Frequency of a particular musical instrumental should be in tune with that of other musical instruments. This helps in production of pleasant music. That is why artists usually adjust the frequencies at the start of a musical concert.