# KSEEB Solutions for Class 8 Science Chapter 14 World of Sounds

## Karnataka Board Class 8 Science Chapter 14 World of Sounds

### KSEEB Class 8 Science Chapter 14 Textual Questions & Answers

I. Four alternatives are given to each of the following incomplete statement/ question. Choose the right answer:

Question 1.
Imagine that you are listening to a popular song from a radio. Using volume control knob, you slightly increase the volume. The factor related to sound wave in this process is increase in.
a. frequency
b. velocity
c. amplitude
d. both frequency and wavelength
c. amplitude

Question 2.
The velocity of sound is highest in.
a. air
b. water
c. glass
d. vacuum
c. glass

Question 3.
In an unoccupied hall of a choultry you will experience the echo effect of sound. If the same hall is furnished with almirahs, tables, chairs and other commodities, you may not experience the echo clearly It is because,
a. Sound waves get absorbed by the objects in the hall
b. the are of reflecting surface decreases
c. reflected sound is reflected again
d. sound does not get reflected
a. sound waves get absorbed by the objects in the hall.

Question 4.
The factor that is transmitted in wave motion is.
a. particles of the medium
b. vibrations of particles
c. energy of the cause of the wave
d. electrons of the medium
a. particles of the medium

II. Fill in the blanks with suitable words:

Question 1.
The product of frequency and wave length of a sound waves is called ………..
velocity

Question 2.
The SI unit of wave length is ………….
Lambda

Question 3.
The velocity of sound in air at 25°C is approximately …………..
346 m/sec

Question 1.
Why is sound a longitudinal wave?
Sound is a longitudinal wave because it is a mechanical wave in which the vibration of particles is parallel to the direction of the sound.

Question 2.
Explain an activity to show that sound can do work.
Take a thin strip of paper. Hold it against sound from a loud speaker the paper starts moving. This shows that sound can do work.

Question 3.
Describe an activity to show that the sound is produced by vibration of materials.
Take a rubber string stretch it tightly between two supports. Pluck the string, the string begins to vibrate. Then we will be able to heard some sound, stop the movement of the string. Even the sound also stops. From this activity we can show that the sound is produced by the vibration of material.

Question 4.
Make a list of five musical instrument, state how each of them produce sound.

 Musical instrument The way it produce sound 1 .Harmonium By the vibration of air 2.Tabla By the vibration of the membrane 3.Sitar By the vibration of string 4.Guitar By the vibration of string 5. Flute By the vibration of air

Question 5.
List two applications of reflection of sound.

1. Ultrasound scanner: This is an invaluable diagnostic tool for examining fluid-filled organs such as bladders, kidneys, etc
2. Eco-ranging: By using an ultrasound signal sent by soar and knowing the velocity of sound in water the depth of the sea can be calculated.

Question 6.
Describe an activity that the sound requires a material medium for its propagation.

Suspend a mobile phone inside an airtight glass bell jar as shown in the diagram connect the bell to a vacuum pump, when a call is made to that phone, the ringing tone is heard. Start removing the air from the jar by using a vacuum pump. The ringing tone feeble and feeble and cannot hear anymore. This experiment shows that sound cannot travel in a vacuum, it needs a material medium for its propagation.

Question 7.
Represent a wave graphically. Show in the diagram, the wavelength, and amplitude.

Question 8.
Why is sound both a boon and a bone?
A pleasant sound like Hello sir/Hello madam while addressing a person or hearing musical notes are boon and a loud sound may cause irritation, headache and loss of concentration. Long exposure to such sounds may lead to loss of sleep, tension and stress, high blood pressure, heart trouble etc. Therefore such sounds are bone to us.

Question 9.
What measures would you take to minimize the sound disturbance caused to others?
The steps to be taken to minimize the sound disturbance are as follows

1. Turn off your electronic systems. When not in use and also to not play them too loudly
2. Soundproof your music playing area.
3. Plant more trees.
4. Regular maintenance of vehicles and machines.
5. Use earplugs.

Question 1.
What is sound?
Sound is a form of energy which excites in our ears the sensation of hearing.

Question 2.
What produces sound?
Sound is produced by a vibrating object.

Question 3.
When do materials produce sound?
Materials generally produce sound when they move back and forth rapidly. We call such motion as ‘Vibration’

Question 4.
How is the sound produced in the Human body?
We have a special apparatus called Larynx or voice box which is located at the upper end of the windpipe. There are two membranes called vocal cords which stretch across the larynx. The narrow slit loft between them controls the passage of air. When we push the air through the slit causes the vocal cords to vibrate which produces the sound.

Question 5.
What are the waves?
Any energy moves through a medium by creating a disturbance in it. These disturbances may repeat themselves at regular intervals. Such periodic disturbances constitute a pattern, are called waves.

Question 6.
What are the transverse waves?
Transverse waves are the waves, on which the particles of the medium vibrate perpendicularly to the line of propagation.
Ex: water waves.

Question 7.
How do Dolphins and whales live in water communicate?
Dolphins and whales produce and use different kinds of sounds and whistles. These sounds travel through water and pass on messages to others. Some species of dolphins send special sounds to identify themselves.

Question 8.
What is meant by wavelength?
The distance between two successive compressions is called the wavelength of the sound wave. This is equal to the distance between two successive rarefaction. The wavelength is represented by Lambda (‘A’)

Question 9.
What is the frequency? Explain.
The number of times an object vibrates in on second is called Frequency. The number of compressions that pass through a point in one second also gives Frequency SI unit of Frequency is ‘hertz’.
The symbol is Hz.  1 hertz (Hz) = 1 wave per second or cycle per second.

Question 10.
What is meant by the amplitude of a sound wave?
The highest displacement of a particle from its rest position is the amplitude of the sound.

Question 11.
What is an Amplifier?
Amplifier is a device that increases the amplitude of a wave.

Question 12.
What is the speed of sound?
Speed of sound is the distance traveled by it in one second. The SI unit of speed is meter per second we write this as ms-1.

Question 13.
What is meant by the Echo?
The reflection of sound is called Echo.

Question 14.
What do you mean by Sonic boom?
When a plane travels faster than the speed of sound the plane breaks the sound barrier and produces a loud sound. This is called the Sonic boom.

Question 15.
Does the experiment show that sound reflects?

There are two identical cardboard tubes P and Q with metal surface AB and screen S between the two tubes as shown in the figure. Keep a small clock at the other end of the tube ‘P’ and ear at the end of the tube Q. The tick-tick of the clock can be heard if the angle is the same.

Question 16.
What is meant by Noise?
Some sound cause disturbance to humans and other animals, such unwanted sound is called Noise, or Unpleasant sound is called Noise [High-frequency sound].

Question 17.
Mention the harmful effects of noise pollution.