Chapter 12. Sound

Class 9 Science Examplar Chapter 12. Sound Choose the correct answers :

Q1. The audible range of sound for human beings extends from about –

(A) 10Hz to 10KHz

(B) 20Hz to 20KHz

(C) 100Hz to 20KHz

(D) 200Hz to 20KHz

Ans : (B) 20Hz to 20KHz

Q2. The sounds of frequencies below 20 Hz are called :

(A) Infrasound or infrasonic sound .

(B) Ultrasound .

(C)  (A) and (B) both

(D) Sonar

Ans : (A) Infrasound or infrasonic sound .

Q3. For hearing a distinct sound, the time interval between the original sound and the reflected one must be at least –

(A)  0.01 s

(B) 0.1 s

(C) 0.5 s

(D) 0.2

Ans : (B) 0.1 s

Q4. The frequency of a source of sound is 100 Hz .How many times does it vibrate in a minute ?

(A) 600 times

(B) 6000 times

(C) 100 times

(D) 1000 times

And : (B) 6000 times

[ Here, F = 100 Hz , T  = 1 min. = 60 s

Number of oscillations = F× T = 100 × 60 =6000 ]

Q5. The time taken by two consecutive compressions or rarefactions to cross a fixed point is called :

(A) the time period of the wave .

(B) the time period of the sound wave .

(C) the amplitude of the wave .

(D) The sound wave .

Ans : (A) the time period of the wave .

Q6. The sounds of frequencies higher than 20 kHz are called :

(A) Infrasound or infrasonic sound .

(B) Ultrasound or ultrasonic sound

(C)  (A) and (B) both

(D) Sonar

Ans : (B) Ultrasound or ultrasonic sound .

Q7. The distance between two consecutive compressions or two consecutive rarefaction is called :

(A) amplitude

(B) Wavelength

(C)  speed

(D) Frequency

Ans : (B) Wavelength

Q8. A sound of single frequency is called :

(A) amplitude

(B) loudness

(C) pitch

(D) tone

Ans : (D) tone

Q9. The audible range of sound for whales and elephants is :

(A) Below 20 Hz

(B) Higher than 20 Hz

(C) Below 20 kHz

(D) Higher than 20 kHz

Ans : (A) Below 20 Hz

Q10. A sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium , then the wavelength is :

(A)  2 m

(B) 3 m

(C) 4 m

(D) 1m

AnS : (A)  2 m

[Here,  Hz ,  m/s

Wavelength  s  ]

Q11. 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

Q12. Akey 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 but 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

Q13. In SONAR , we use

(A) ultrasonic waves

(B) infrasonic waves

(C) radio waves

(D) audible sound waves

Ans : (A) ultrasonic waves

Q14. 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 particle as well as disturbance travel from one place to another.

Ans : (C) disturbance moves

Q15. When we change feeble sound to loud sound we increase its

(A) frequency

(B) amplitude

(C) velocity

(D) wavelength

Ans : (B) amplitude

Q16. In the curve(Fig. 121) half the wavelength is :

(A) A B

(B) B D

(C) D E

(D) A E  

Ans : (B) B D

Q17. 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

Q18. Infrasound can be heard by

(A) dog

(B) bat

(C) rhinoceros

(D) human beings

Ans : (C) rhinoceros

Q19. 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

Class 9 Science Examplar Chapter 12. Sound Fill in the blanks :

20.  is produced due to vibration of different objects .

Ans : Sound .

Q21. Sound cannot travel in  .

Ans : vacuum .

Q22. The persistence of sound in an auditorium is the result of repeated reflections of sound and is called  .

Ans : reverberation .

Q23.  Is a physiological response of the ear to the intensity of sound .

Ans : Loudness .

Q24. The amount of sound energy passing each second through unit area is called the  of sound .

Ans : intensity .

Q25. The sensation of sound persists in our brain for about  .

Ans : 0.1 second .