Class 9 Science

Chapters

# Sound

## Exemplar Problems

### Multiple Choice Questions

Question 1: Note is a sound

1. of mixture of several frequencies
2. of mixture of two frequencies only
3. of a single frequency
4. always unpleasant to listen

Answer: (a) of mixture of several frequencies

Question 2: A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case

1. sound will be louder but pitch will not be different
2. sound will be louder and pitch will also be higher
3. sound will be louder but pitch will be lower
4. both loudness and pitch will remain unaffected

Answer: (d) both loudness and pitch will remain unaffected

Question 3: In SONAR, we use

1. ultrasonic waves
2. infrasonic waves
4. audible sound waves

Question 4: Sound travels in air if

1. particles of medium travel from one place to another
2. there is no moisture in the atmosphere
3. disturbance moves
4. both particles as well as disturbance travel from one place to another.

Question 5: When we change feeble sound to loud sound we increase its

1. Frequency
2. Amplitude
3. Velocity
4. Wavelength

Question 6: In the curve (Figure) half the wavelength is

1. A B
2. B D
3. D E
4. A E

Question 7: Earthquake produces which kind of sound before the main shock wave begins

1. Ultrasound
2. Infrasound
3. audible sound
4. none of the above

Question 8: Infrasound can be heard by

1. Dog
2. Bat
3. Rhinoceros
4. Human beings

Question 9: Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting

1. intensity of sound only
2. amplitude of sound only
3. frequency of the sitar string with the frequency of other musical instruments
4. loudness of sound

Answer: (c) Frequency of the sitar string with the frequency of other musical instruments

## Matter in Our Surroundings

Anything that has both mass and volume is called matter. You can also say that anything which has mass and which occupies space is called matter.

## Is Matter Around Us Pure?

Elements and compounds are pure substances. All other substances are mixtures which means they are not pure substances.

## Atoms and Molecules

Read about law of conservation of mass, law of constant proportions and Dalton's atomic theory.

## Structure of Atoms

Atom is made of three particles; electron, proton and neutron. These particles are called fundamental particles of an atom or sub atomic particles.

## Cell: The Fundamental Unit of Life

A cell is capable of independent existence and can carry out all the functions which are necessary for a living being.

## Tissue

A groups of cells which is meant for a specific task is called tissue. Tissues are the first step towards division of labour in complex organisms.

## Diversity in Living Organisms

Without proper classification, it would be impossible to study millions of organisms which exist on this earth.

## Motion

If an object changes its position with respect to a reference point with elapse of time, the object is said to be in motion.

## Force & Laws of Motion

Force has numerous effects. Force can set a stationary body in motion. Force can stop a moving body.

## Gravitation

Earth attracts everything towards it by an unseen force of attraction. This force of attraction is known as gravitation or gravitation pull.

## Work & Energy

When force is exerted on an object and object is displaced, work is said to be done. It means work is the product of force and displacement.

## Sound

Sound is a type of energy. Sound travels in the form of wave from one place to another.

## Why Do We Fall Ill

Health is a state of physical, mental and social well being. A condition in which the affected person is unable to carry out normal activities is termed as disease.

## Natural Resources

Resources which are obtained from nature are called natural resources. Examples: Air, water, soil, wood, etc.

## Improvement in Food Production

Food security is said to exist when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.