Science In Everyday Life Solutions for Class 8 Science Chapter 12 Sound are provided here with simple step-by-step explanations. These solutions for Sound are extremely popular among class 8 students for Science Sound Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science In Everyday Life Book of class 8 Science Chapter 12 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science In Everyday Life Solutions. All Science In Everyday Life Solutions for class 8 Science are prepared by experts and are 100% accurate.

Page No 172:

Question 1:

How are sound waves produced?

Answer:

Sound waves are produced due to vibration (back and forth movement of a body about a central position) of molecules of a medium (gas, liquid or solid).

Page No 172:

Question 2:

Name two factors on which the speed of sound depends.

Answer:

Speed of sound depends on:

  1. The density of the material through which sound travels.
  2. The nature of the medium through which sound travels.

Page No 172:

Question 3:

What is the ' time period' of an oscillation?

Answer:

Time period of an oscillation is the time taken to complete one oscillation and is measured in seconds.

Page No 172:

Question 4:

What is the audible range of frequency of sound waves for human beings?

Answer:

The audible range of sound for human beings is between 20 Hz to 20,000 Hz.

Page No 172:

Question 5:

Name three types of musical instruments.

Answer:

The three types of musical instruments are:

  1. Stringed instruments
  2. Wind instruments
  3. Percussion instruments

Page No 172:

Question 6:

Give two harmful effects of noise pollution.

Answer:

Two harmful effects of noise pollution include loss of concentration and sleep disturbance.

Page No 172:

Question 1:

How do human beings produce sound while talking?

Answer:

In human beings, sound is produced by the voice box or larynx, which is located at the upper end of the wind pipe. The production of sound is controlled by vocal cords that are thin membranes stretching across the voice box. Muscles are attached to the vocal cords. With the help of these muscles the tension in the vocal cords can be varied and they can become tight or loose, thereby producing sound.

Page No 172:

Question 2:

Explain how sound waves travel in air.

Answer:

Sound travels through air when air molecules vibrate. If air molecules are considered as small balls, a sound wave travels through air by pushing these balls close to each other and then pulling them away from each other. The air molecules come together in areas called compressions and they lie away from each other in areas called rarefactions. The air molecules do not move from their place but only vibrate about their original position. This vibrating effect propagates and allows sound to travel through air.

Page No 172:

Question 3:

Explain briefly how the ear works, and therefore how we 'hear'.

Answer:



Human ear is made of three parts:

  • Outer ear – This is the visible part called pinna. It collects sound waves and directs them to the ear tube, at the end of which lies the ear drum. When sound strikes, the ear drum vibrates and passes sound to the middle ear.
  • Middle ear – It is a cavity containing three important bones, placed in a manner that they can move with the vibrating ear drum and transmit sound to the inner ear.
  • Inner ear – It contains fluid, which vibrates with transmission of sound and excites tiny hair in inner ear. The hair transform these vibrations into electrical impulses and these are transmitted to the brain through auditory nerve.

Page No 172:

Question 4:

Explain the three categories of musical instruments.

Answer:

The three categories of musical instruments are:

  • Stringed instruments – These instruments have an air chamber to enable increasing the loudness of the sound produced by plucking strings. The pitch is altered by altering the length of the vibrating portion of string. E.g. guitar, sitar, violin
  • Wind instruments – In this sound is produced by vibrating air column within the instrument. The pitch is altered by altering the length of vibrating air column. E.g. flute, trumpet, harmonica.​
  • Percussion instruments – Sound is produced by vibrating skin or membrane. Pitch can be altered to some extent by increasing or reducing the tension of membrane or by changing the force with which the membrane is struck. E.g. tabla, drum and dholak.

Page No 172:

Question 5:

What is noise? What is noise pollution? What measures should we take to reduce noise pollution?

Answer:

Noise is any unpleasant sound from any source that causes psychological and/or physiological discomfort. Noise can have harmful effects like irritability, lack of concentration, sleep disturbance and stress. Noise pollution is the sustained presence of unwanted, harmful and annoying noise in the environment. E.g., automobiles, television, blaring loudspeakers, air coolers, etc. Measures to reduce noise pollution include:

  • avoid use of loudspeakers
  • restrict talking too loudly or playing television too loudly in houses.
  • avoid playing loud music while driving and the use of horns unnecessarily.  

Page No 172:

Question 1:

Define/Explain the following.
1. Vibration
2. Amplitude
3. Ultrasonic waves
4. Noise
5. Noise pollution

Answer:

  1. Vibration is a rapid back and forth movement of a body about a central position.
  2. Amplitude of an oscillation is the maximum displacement of the bob from its mean position during oscillation.
  3. Ultrasonic waves are sound frequencies above 20,000 Hz, which humans cannot hear these waves.
  4. Noise is any unpleasant sound from any source that causes psychological or physiological discomfort.
  5. Noise pollution is the sustained presence of unwanted, harmful and annoying noise in the environment.

Page No 172:

Question 1:

Which of the following is a unit of frequency?
(a) meter
(b) per metre
(c) second
(d) per second

Answer:

(d) per second
The SI unit of frequency is 'per second' called Hertz.

Page No 172:

Question 2:

A body vibrating with a higher frequency will
(a) have a lower pitch
(b) have a higher pitch
(c) be louder
(d) be softer

Answer:

(b) have a higher pitch
Higher the frequency, higher is the pitch.

Page No 172:

Question 3:

Sound can travel in
(a) solid
(b) liquid
(c) gas
(d) all of the these

Answer:

(d) All of these
Sound needs a medium like solids, liquids or gases to travel as it travels through vibrations in molecules. It cannot travel in vacuum.

Page No 172:

Question 4:

Sound waves with a frequency below 20 Hz are called
(a) infrasonic waves
(b) ultrasonic waves
(c) ultrasound
(d) none of these

Answer:

(a) infrasonic waves
Infrasonic waves are sound waves with frequency below 20 Hz.

Page No 172:

Question 5:

Noise pollution can be caused by
(a) polluted air
(b) traffic noise
(c) blaring loud speakers
(d) Both (b) and (c)

Answer:

(d) Both b and c
Traffic noise and blaring loud speakers can cause noise pollution.

Page No 172:

Question 1:

Fill in the blanks with the correct words.
1. Sound is produced because of .................... (vibrations/refractions).
2. Sound travels through air by means of .................... (compressions/depressions) and .................... (rarefactions/refractions).
3. Sound needs a .................... (medium/vacuum) to travel.
4. The .................... (pinna/ear drum) collects sound waves and directs them to the ear tube.
5. The speed of sound is .................... (same/different) in different substances.

Answer:

  1. Sound is produced because of vibrations.
  2. Sound travels through air by means of compressions and rarefactions.
  3. Sound needs a medium to travel.
  4. The pinna collects sound waves and directs them to the ear tube.
  5. The speed of sound is different in different substances.



View NCERT Solutions for all chapters of Class 8