Reflection of Sound and Echo - UNSOLVED PRACTICE SET

Q7. State the law of reflection of sound. How is it similar to the law of reflection of light?

Q8. What is an echo? What are the two conditions necessary for a distinct echo to be heard?

Q9. Why is the minimum distance for an echo 17 m (when speed of sound = 340 m/s)? Show the calculation that leads to this value.

Q10. What is reverberation? How is reverberation different from echo? Why is too much reverberation a problem in lecture halls and cinema theatres?

Q11. Explain how SONAR works. How does a ship use SONAR to measure the depth of the ocean floor?

Q12. Walls of concert halls, auditoriums, and cinema theatres in India are often lined with soft materials, carpets, and curtains. Explain the scientific reason for this design choice.

Q13. Explain the phenomenon of echo in detail. Your answer must cover:
(a) the law of reflection of sound,
(b) the condition of minimum distance (17 m) and show how it is derived using time of persistence = 0.1 s and v = 340 m/s,
(c) why we do not hear echo in a small room even though sound does reflect,
(d) why mountain valleys produce multiple echoes, and
(e) one practical application of echo in technology.

Q14. A ship's SONAR sends a pulse of ultrasound toward the ocean floor and detects the echo after 3.2 seconds.
(a) If the speed of sound in seawater is 1520 m/s, calculate the depth of the ocean at that point.
(b) The ship moves over a submarine wreck and the echo returns in 2.4 s. Calculate the height of the wreck from the ocean floor.
(c) Explain why SONAR uses ultrasound rather than ordinary audible sound.
(d) Name two other animals besides bats that use echolocation.
(e) How is SONAR used by the Indian Navy?

Q15. Compare echo and reverberation in detail:
(a) definitions of both,
(b) the distance and time conditions for each,
(c) why reverberation is desirable to some extent in a music concert hall but harmful in a school classroom,
(d) how architects design auditoriums to control reverberation (name at least three design features), and
(e) describe one real Indian auditorium or hall and discuss how its acoustic design helps sound quality. 

Q16. A student shouts toward a large cliff and hears the echo after 2.4 seconds. The speed of sound in air is 340 m/s.
(a) Calculate the distance between the student and the cliff.
(b) If the student moves 68 m closer to the cliff and shouts again, after how many seconds will the echo be heard?
(c) What is the minimum distance from the cliff at which a distinct echo can be heard?
(d) If the student stands only 10 m away, will they hear an echo? Explain why or why not.

Q17. A bat flying in a dark cave emits ultrasonic pulses. It detects an echo from a moth after 0.006 seconds. Speed of sound = 340 m/s.
(a) Calculate the distance between the bat and the moth.
(b) The bat is flying toward the moth at 5 m/s. After 1 second, how far is the moth from the bat?
(c) How long will the echo now take to return?
(d) Explain why bats use ultrasound rather than normal sound for echolocation.

Q18. An architect is designing a new auditorium in Bengaluru. The hall is 25 m long, 20 m wide, and 10 m high.
(a) Calculate the time for sound to travel from one end of the hall to the other (speed of sound = 340 m/s).
(b) Can an echo be heard inside this hall? Explain using the minimum echo distance.
(c) What phenomenon will occur instead of echo in this hall?
(d) The architect uses sound-absorbing panels on the walls. What effect does this have on the reverberation? 

(e) Why is controlling reverberation important for speech clarity in a lecture hall?