Class 09 Physics Chapter - Sound, Reflection of sound CBSE and board questions with answer
Q. A strong transverse pulse is created in one end of a string. It completes 10 journeys along its length; before fading out. The initial reading of the stop clock used in the experiment was 25s and the final reading was 75s. If the length of the string for one journey is L meter, the speed of the pulse through the string?
Ans: The time taken for one journey is (75 -25)/10 second. The length of the string is L meter So, the speed of the pulse, through the string, is: L/5
Q. What is the velocity of pulse for slinky when it takes 5 sec to travel from point A to B and back to A . Distance between A to B is 5 m
Ans : Wave length = d = 5 + 5 = 10m and t = 5 sec.
Q. How does the ear drum of human ear vibrate ?
Ans: When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates.
Q. What is the role of hammer bone, anvil bone, stirrup bone and cochlea of human ear in hearing a sound
Ans: The vibrations due to the ear drum is amplified several times by three bones in the middle ear. The pressure variations in the inner ear turned in to electrical signals by the cochlea.
Q. . At any instant a compression is formed at a point. After how much time period (i) A rarefaction (ii) A compression Will be formed at the same point?
Ans: (a) (b) t
Q. Hari and Shivam were playing on identical guitars whose strings were adjusted to give notes of the same pitch. Which of two, the quality of the two notes and frequencies be the same. Give reason for your answer.
Ans : Frequencies of both will be the same as strings were adjusted to give notes of the same pitch. Quality will be also the same as they are identical guitars
Q. Why do we hear sound produced by the humming bees while the sound of vibrations of pendulum is not heard?
Ans: Reason: Vibration of wings of a bee is higher than 20Hz where as the vibration of pendulum is less than 20Hz
Q. . When the wire of a guitar is plucked, what types of waves are produced in (i) air and (ii) wire? Give reasons in support of your answer. Ans: (i) air – Longitudinal wave as the particles vibrate in a direction which is parallel to the direction of the wave (ii) Wire – transverse wave as the particles vibrate in a direction which is perpendicular to the direction of the wave.