1

What do you mean by echo and state 2 conditions for an echo to be heard distinctly?

2

State the application of echo by a bat, dolphin, fisherman, etc.

3

What is SONAR? State the principle on which it is based.

4

Numerical sum based on:
v= d/t (when echo is not mentioned in the
question)
v= 2d/t (when echo is mentioned in the
question)

5

A man standing 25 m away from a wall produces a sound and receives the reflected sound:

• Calculate the time after which he receives the reflected sound, if the speed of sound in air is 350 m/s. 
• Will the man be able to hear a distinct echo? Give a reason. 

6

A man standing in front of a cliff fires a gun. An echo is heard after 3 s. On moving 80 m closer to the cliff, he again fires a gun and hears an echo after 2.5 s. Calculate:

(a) The distance of man from the cliff to his initial position. 

(b) The speed of sound.

7

What do you mean by natural vibrations of a body? Draw a graph between displacement and time of a body executing the natural vibration. State one condition for a body to execute the natural vibration.

8

State the factors on which the frequency depends for the following:

• Stringed instruments {Freq a (1/1) }
• Bob of a simple pendulum
• Load suspended from a spring
• Air column in a flute
• Organ pipe open at both end (1:2:3)
• Organ pipe with one end closed (1:3:5)

9

What is the purpose of strings of different thickness in a stringed instrument?

10

Write down the differences between free and forced vibrations with corresponding examples. Also draw a sketch showing the displacement against time for a body executing the damped vibrations.

11

What is meant by resonance? What is the condition necessary for resonance to take place?

12

Write down the application of resonance in the case of:

• Tuning fork of same frequency
• Resonant vibrations of pendulum of same length suspended from the same elastic support.
• Air column when a long cylindrical tube is connected with a cylindrical vessel which acts as a reservoir.
• Machine parts when at a certain speed of the vehicle that particular part of the frame starts vibrating vigorously.
• Stretched string and sound box of musical instruments and sonometer.
• Troops cross a suspension bridge
• Test tubes of the same height which are filled with water up to different heights.

13

Give comparison of sound on the basis of 3 characteristics, i.e. loudness, pitch and quality and their subjective nature.

14

Define loudness. Name the corresponding measurable quantity. 

15

Mention the factors of loudness and intensity.

16

The bells of a temple are big in size. Why?

17

What is the unit for sound level? 

18

What is the unit of loudness? 

19

Define Pitch. Give its measurable quantity.

20

The ratio of amplitude of 2 waves having the same pitch is 3:4. What is the ratio of their:

• Loudness (directly proportional to a square) 
• Frequency 

21

How is it possible to detect the filling of a bottle under a water tap by hearing the sound at a distance?

22

Define quality of sound. 

23

Which characteristic of sound makes it possible to recognize a person from his voice without seeing him?

24

Differentiate between musical note and a noise.

25

Technical name of the musical instrument Flute is an organ pipe. If the pipe is open at one end (closed pipe), then its fundamental frequency is V/4| and if it is open at both ends then its fundamental frequency is V/2I. What will be the impact on quality of sound?