Class-10 Goyal Brothers Sound ICSE Physics Solutions Ch-7. We Provide Step by Step Answer of Exercise, MCQs, Numerical Problem Questions of Exercise-1 Goyal Brothers Sound ICSE Class-10 . Visit official Website CISCE  for detail information about ICSE Board Class-10 Physics.

## Sound Class-10 Goyal Brothers ICSE Physics Solutions Ch-7

-: Select Topics :-

Exercise-1

MCQ -1

Numerical Problem-1

Exercise-2

Exercise-3

### Exe-1 Class-10

Sound Goyal Brothers ICSE Physics Solutions Ch-7

Question 1.
(a) State the laws of reflection of sound.
(b) How will you verify laws of reflection of sound experimentally ?
(a) Laws of reflection of sound :

1. Angle of incidence is equal to the angle of reflection. ∠i = ∠l
2. Incident wave, reflected wave and the normal lie in the same plane.

(b) Verification of laws of reflection : Take a smooth polished large wooden board and mount it vertically on a table. At right angle to the board fix a wooden screen on each side of the screen place a long, narrow and highly polished tube from inside. Place a watch at the end A. Move the tube B slightly left or right till distinct tick of water is heard. Measure ∠PKN and
∠BKN.

It is found that ∠PKN = ∠BKN. This verifies the laws of reflection.

Question 2.
Describe any two applications of reflection of sound.
(i) Megaphone : People use horn shaped metal tubes commonly called megaphones while addressing a group of people in fairs or tourist spots. Sound energy is prevented from spreading out by successive reflections from the horn shaped tubes.
(ii) Hearing aid : Its shape is like a trumpet the narrow end is kept in the ear tube of the person who is hard of hearing. Where as the wider end towards the speaker collects the waves and reflects into the narrow end. This increases the intensity of sound energy hence the person who is hard of hearing can hear clearly.

Question 3.
(a) What is an echo ?
ECHO : “The repeated sound heard after reflection from a distant rigid obstacle (such as cliff, a hill side, wall of a building, edge of forest etc.) after the original sound has ceased is called an ECHO.”

(b)
State two conditions necessary for the formation of an echo.
Two conditions for forming an echo :

1. The minimum distance between the source of sound and the reflecting body should be 17 metres.
2. The intensity of sound should be sufficient so that it can be heard after reflection.

Question 4.
What are reverberation ? Give two examples.
Reverberation : “Due to repeated reflections at the reflecting surface (reflector is less than 17 metres from original sound) the sound gets prolonged, This effect is known as reverberation.”
Example :

1. Speaking in a large empty room.
2. Clapping in tombs like TajMahal.

Question 5.
How will you determine speed of sound by the method of echos ?
In order to determine the speed of sound in air, sound produced from a place at known distance d at least 50 m from the reflecting surface. The time interval t in which the echo reaches the place from where sound was produced is noted by a stop watch. Then speed of sound is calculated
as v = total distance travelled /time interval = 2d/ t ms-1

Question 6.
What is sonar ? State its principle. How is it used to find the depth of sea ?
SONAR : “Sound Navigation and Ranging.” It is based on the principle of ECHO.

ultra- sonic waves are sent in all directions from the ship and then are received on their return after reflection. Using the formula an obstacle such as enemy submarine, ice berg, a sunken ship etc. The time interval between sending and receiving of wave is noted. The distance (depth) can be calculated by vis speed of ultrasonic waves in water. v = 2d/t or d = Vt/2

Question 7.
How do bats locate their prey ? Explain in detail.
Location of prey by bats :
Bats can produce and detect the sound of very high frequency up to 10 kHz. The sound produced by bats get reflected back from an obstacle in front of it. These echoes tell the bat how they must turn in the air to avoid collision with obstacles. By using their ears, the bats, can fly skilfully at night in the utter darkness of caves. The highly sensitive nose of a bat acts as a recorder and picks up air vibrations set in motion by the movements of other animals. It appears that the nose and ears of the bats are important factors in the radar like operation.

Question 8.
How do the following use echoes ?

1. army,
2. geologists,
3. fishermen.

(i) army : Echoes are used by army to locate the gun position of enemy. Radar an instrument is used to locate an enemy air-craft ship.
(ii) geologists : Echoes are used by geologists for mineral prospecting.
(iii) fishermen : for locating fishes ultrasonic waves are sent into water. If these vibrations strike a fish, they are reflected back to the receivers. The time for hearing the echoes recorded. The position of fish is calculated by d = v × t/2 using vel. of sound in water as 1450 ms-1.

### Multiple Choice Questions-1

Sound Class-10 Goyal Brothers  ICSE Physics Solutions

Question 1.
The practical application based on the reflection of sound is:
(a) megaphone
(b) sounding board
(c) sonometer
(d) both (a) and (b)
(d) both (a) and (b)

Question 2.
Which is not the condition for the formation of echoes ?
(a) Minimum distance between the source of sound and reflecting body should be 17 m.
(b) The temperature of air should be above 20°C.
(c) The wavelength of sound should be less than the height of the reflecting body.
(d) The intensity of sound should be sufficient so that it could be heard after reflection.
(a) Minimum distance between the source of sound and reflecting body should be 17 m.

Question 3.
For hearing an echo, the minimum distance between the source of sound and reflecting body should be
(a) 12 m
(b) 24 m
(c) 17 m
(d) 51 m
(c) 17m

Question 4.
To locate its prey in the darkness the owl or the bat emits:
(a) infrasonic waves
(b) ultrasonic waves
(c) sonic waves
(d) infrared waves
(b) ultrasonic waves

### Numerical Problem on Echoes

Sound Class-10 Goyal Brothers  ICSE Physics Solutions

Practice Problems 1

Question 1.
A person fires a gun in front of a building 167 m away. If the speed of sound is 334 ms-1, calculate time in which he hears an echo.
d = 167 ∴ 2d = 167 × 2 m
Speed of sound = 334 ms-1
t for echo to be heard = ?

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