Sound - Important Questions Model Question Paper 1 In 9th Science | QB365

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Sound - Important Questions Model Question Paper 1 In 9th Science

Published on: 02/08/2018

Some of the important questions are prepared from this chapter Sound. The important questions are covers from the Higher Order Thinking Questions and Value based questions.

Download CBSE Class 9th Standard CBSE Science question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 9th Standard CBSE Science

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Std: 9th Standard CBSE - Science

chapter: - Model Question paper

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Questions:

Generic 4

1 x 4 = 4

Define the terms time period and frequency of an oscillating body. Give their units and write the relation between them.

Generic 3

2 x 3 = 6

Distinguish between mechanical and electromagnetic waves.

State some important characteristics of wave motion.

Generic 2

3 x 2 = 6

Name two sound waves inaudible to human beings. Give the range of their frequencies.

Write two points of difference between sound wave and light wave.

What are mechanical or elastic waves? Give examples.

Multiple Choice Question

3 x 1 = 3

The product of time period and frequency is

(a)

zero

(b)

unity

(c)

infinity

(d)

none of these

A tuning fork is vibrating in air. The number of compressions going past a given point per second is the

(a)

wavelength

(b)

time-period

(c)

frequency

(d)

amplitude

The reciprocal if frequency is

(a)

amplitude

(b)

wavelength

(c)

time-period

(d)

wave velocity

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Answers Key:

Generic 4

1 x 4 = 4

Time period. The time taken by an oscillating body to complete one oscillation is called its time period. It is denoted by T. Its SI unit is second (s).
Frequency. The number of oscillations or vibrations completed by an oscillating body in one second is called its frequency. It is denoted by v (Greek letter nu).
SI unit of frequency=per second (s^-1) = cycles per second (cps) = hertz (Hz).
Relation between time period and frequency:
Let T=time period of an oscillating body. Then number of oscillations completed in T second = 1
Number of oscillations completed in 1 second =\(\frac { 1 }{ T } \)
But number of oscillations completed in 1 second = frequency (v)
∴ \(v=\frac { 1 }{ T } \)
Hence frequency is equal to the reciprocal of time period.

Generic 3

2 x 3 = 6

Differences between mechanical and electromagnetic waves.

Mechanical waves	Electromagnetic waves
1. These waves require a material medium for their propagation.	1. These waves do not require a material medium for their propagation.
2. These are caused due to vibrations of the particles of the medium.	2. These are caused due to varying electric and magnetic fields.
3. These waves have low speeds, e.g. speed of sound in air is 332 m/s at 0°C.	3. These waves travel with a very speed of \(3\times 10^{ 8 }\quad m/s\) through vacuum.
4. These waves have usually low frequency and large wavelengths.	4. These waves have usually high frequency and low wavelength.
5. These can be transverse or longitudinal.	5. These are only transverse waves.

Characteristics of wave motion:
(i) It is the disturbance which travels forward through the medium and not the particles of the medium, the particles of the medium merely vibrate about their mean positions.
(ii) Each particle receives vibrations a little later than its preceding particle.
(iii) The velocity with which wave travels is different from the velocity of the particles with which they vibrate about their mean positions.
(iv) The wave velocity remains constant in a given medium while the particle velocity changes continuously during its vibration about mean position.

Generic 2

3 x 2 = 6

Infrasonic waves. Sound waves with frequencies less than 20 Hz are called infrasonic waves. Such waves are produced by large vibrating bodies. The earthquakes, volcanic eruptions, big animals like whales and elephants produce infrasonic waves. We cannot hear these waves.
Ultrasonic waves. Sound waves with frequencies greater than 20,000 Hz are called ultrasonic waves or ultrasound. Bats, dogs, rats, cats, birds and insects can produce and also hear these waves. We cannot hear these waves.

Difference between a sound wave and lightwave:

Sound wave	Lightwave
1. It travels in the form of longitudinal waves.	1. It travels in the form of transverse wave.
2. It requires a medium for its propagation.	2. It does not require a medium for its propagation.
3. It travels through air with a speed of 332 m/s at 0°C	3. It travels through air with a speed of nearly \(3\times 10^{ 8 }\quad m/s\) .

Mechanical waves. The waves which require a material medium for their propagation are called mechanical waves. They are also called elastic waves because their propagation depends on the elastic properties of the medium.
Examples of mechanical waves:
(i) Sound waves in air.
(ii) Waves over water surface.
(iii) Waves produced during earthquake. These are known as seismic waves.

Multiple Choice Question

3 x 1 = 3