Chapter 12: Sound

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

Soln:

Answer is (a) of mixture of several frequencies

Explanation:

Sound is a mixture of several frequencies which can be produced by vibrating objects.

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 the pitch will not be different

(b) sound will be louder, and the pitch will also be higher

(c) sound will be louder, but the pitch will be lower

(d) both loudness and pitch will remain unaffected

Soln:

Answer is (a) sound will be louder, but the pitch will not be different

Explanation:

Pitch depends on the frequency particular key, and loudness depends on the force by which the key is pressed.

3. In SONAR, we use

(a) ultrasonic waves

(b) infrasonic waves

(c) radio waves

(d) audible sound waves

Soln:

Answer is (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.

Soln:

Answer is (c) disturbance moves

Explanation:

Sound waves propagate by vibrating in their own position. Whereas disturbance created by the vibration of particles moves from one place to another.

5. When we change feeble sound to loud sound, we increase its

(a) frequency

(b) amplitude

(c) velocity

(d) wavelength

Soln:

Answer is (b) amplitude

Explanation:

The Loudness of sound is proportional to amplitude. When amplitude increases, feeble sound changes to loud sound.

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

(a) A B

(b) B D

(c) D E

(d) A E

Soln:

Answer is (b) B D

Explanation:

Wavelength is the distance between two consecutive troughs. In the graph half, the wavelength will be BD.

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

Soln:

Answer is (b) infrasound

Explanation:

It is due to infrared rays, few animals sense the earthquake, and they behave abnormally before the earthquake.

8. Infrasound can be heard by

(a) dog

(b) bat

(c) rhinoceros

(d) human beings

Soln:

Answer is (c) rhinoceros

Explanation:

Infrasound has a frequency less than 20 Hz, and Rhinoceroses communicate using Infrasound waves of the frequency of 5 Hz hence rhinoceros is the right answer.

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

Soln:

Answer is (c) frequency of the sitar string with the frequency of other musical instruments

Explanation:

Artists adjust the frequencies before beginning to play instruments because musical instruments should be tuned in with other musical instruments to produce pleasant music.