Ncert – class 9- science – Chapter 11 – Sound 2 Welcome to your Ncert – class 9- science – Chapter 11 – Sound 2 1. An underwater sonar source operating at a frequency of 60 kHz directs its beam towards the surface. If the velocity of sound in air is 330 m/s, the wavelength and frequency of waves in air are: 5.5 mm, 20 kHz 330mm, 60 kHz 5.5 mm, 60 kHz 5.5 mm, 80 kHz None 2. Which one of the following material will reflect sound better? Thermocole Steel Paper Curtain made from cloth None 3. Which of the following is/are correct statement(s)?(1) Besides helping in finding the distance of an object, SONAR also indicates its direction and speed.(2) Megaphone is a device that works on the ~ principle of reflection of sound.(3) Ultrasonics are used to detect earthquakes.(4) Like light, sound waves also obey laws of reflection. 1,2,4 1,2,3 1,3,4 2,3,4 None 4. The time period of a vibrating body is 0.02s. The frequency of the vibrating body will be 20Hz 1Hz 50Hz 100Hz None 5. The time period of the second hand in a clock is : 2 hours 1 minute 1 hour 24 hours None 6. A man pronounces a, b, c, d and e and hears last four syllables as an echo. Taking velocity of sound as 340 ms-1 , the distance of reflecting surface, if it takes one-fifth of a second to pronounce or hear one syllable is 613 m 340 m 316 m 136 m None 7. When a tuning fork produces sound waves in air, which one of the following is the same in the material of tuning fork as well as in air ? Amplitude Wave length Frequency Velocity None 8. The minimum distance between the source of the sound and the obstacle for an echo (at 20ºC) to take place is : 1.72m 17.8m 34.4m 17.2m None 9. The loudness of sound decreases with an:(1) Increase in the distance between the ear and the source(2) Decrease in the amplitude of the vibrating body(3) Increase in frequency of sound(4) Decrease in frequency 2 and 3 1 and 2 1,3 and 4 1 and 4 None 10. Three different vibrating bodies produce three types of sounds X, Y, and Z.Sounds X and Y cannot be heard by a man having a normal range of hearing but sound Z can be heard easily. The sound X is used to find faults and cracks in metals. The sound is similar to that which is produced during an earthquake before the main shock wave is generated.Name one device which can produce sound like X. Ear mufflers SONAR Bulb horn Megaphone None 11. A person standing between a pair of tall and wide cliffs claps his hands. He hears the first two echoes at 2 sec and 3 sec respectively. If the speed of sound is 330 m/sec, then every third echo is the loudest The time of third echo is 5 second Separation between the cliffs is 825m after the second echo,none is formed None 12. Identify the longitudinal waves from the following Radio waves Light waves Ultrasonic waves Surface water waves None 13. An echo is heard because of the persistence of _____________ hearing is 0.1 s vision is 0.1 s hearing is 0.5 s vision is 0.8 s None 14. When a tuning fork is striked using a rubber prong, the compressions and rarefactions in the sound wave correspond to Both are low density regions Low pressure and high pressure regions High pressure and low pressure regions Both are high density regions None 15. A person is in front of a vertical mountain fires a bullet and hears its echo after a time 3 s. The person walks a distance 'd' towards mountain then fires another bullet and hears its echo after a time 2 s. If velocity of sound in air is 340 ms-1 , the value of 'd' is 85 cm 340 m 170 m 255 m None Time's up Please Share This Share this content Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Leave a Reply Cancel replyCommentEnter your name or username to commentEnter your email address to commentEnter your website URL (optional) Save my name, email, and website in this browser for the next time I comment.
