Science Que-Ans (Each of 5 Mark )

When an object vibrates (and makes sound), then the air layers around it also start vibrating in exactly the same way and carry sound waves from the sound producing object to our ears. Suppose a tuning fork is vibrating and producing sound waves in air. Since the prongs of the tuning fork are vibrating, the individual layers of air are also vibrating. Sound travels in the form of longitudinal waves in which the back and forth vibrations of the air layers are in the same direction as the movement of sound wave.

A compression is that part of a longitudinal wave in which the particles of the medium are closer to one another than they normally are, and there is a momentary reduction in volume of the medium. A rarefaction is that part of a longitudinal wave in which the particles of the medium are farther apart than normal, and there is a momentary increase in the volume of the medium. Longitudinal waves consist of compressions and rarefactions.

Reverberations in a big hall or auditorium can be reduced by the following methods:

1. Panels made of sound absorbing materials are put on the walls and ceilings of hall and auditorium.
2. Carpets are put on the floor to absorb sound and reduce reverberations.
3. Heavy curtains are put on doors and windows to absorb sound and reduce reverberations.
4. The seats in the hall are made from materials having sound absorbing properties.

1. The person would hear a lot of noise in heavy city traffic. Hence, he can conclude that he was in a city.
2. The person would hear a very little noise in village traffic. Hence, he can conclude that he was in a village.
3. The person would hear echoes when talking in a bare room.
4. In furnished room, echo is very less. Hence, he can conclude that he was in a furnished room.

A compression is that part of a longitudinal wave in which the particles of the medium are closer to one another than they normally are, and there is a momentary reduction in volume of the medium. It is a region of high pressure. A rarefaction is that part of a longitudinal wave in which the particles of the medium are farther apart than normal, and there is a momentary increase in the volume of the medium. It is a region of low pressure.

Longitudinal wave: A wave in which the particles of the medium vibrate back and forth in the ‘same direction’, in which the wave is moving, is called a longitudinal wave. These waves can be produced in all the three media: solids, liquids and gases. Transverse wave: A wave in which the particles of the medium vibrate up and down, ‘at right angles’ to the direction in which the wave is moving, is called a transverse wave. It can be produced in solids and liquids but not in gases.

Longitudinal waves:

1. The waves which travel along a spring when it is pushed and pulled at one end.
2. Sound waves in air.

Transverse waves:

1. The waves produced by moving one end of a long spring up and down rapidly, while other end is fixed.
2. The water waves or ripples formed on the surface of water in a pond.

Fill water in a beaker up to its brim. Touch the surface of water with the prongs of a sound making tuning fork (which has been struck on a hard rubber pad). The prongs of tuning fork producing sound splash water. This shows that the prongs of a sound producing tuning fork are vibrating (moving forwards and backwards rapidly).

The prongs of a sound producing tuning fork splash water, so they are vibrating.

Soundboard: The soundboard is a concave board (curved board) which is placed behind the speaker in large halls or auditoriums so that his speech can be easily heard even by the persons sitting at a considerable distance.
The sound board works as follows: the speaker is made to stand at the focus of the concave soundboard. The concave surface of the soundboard reflects the sound waves of the speaker towards the audience (and hence prevents the spreading of sound in various directions). Due to this, sound is distributed uniformly throughout the hall and even the persons sitting at the back of the hall can hear the speech easily.

First the sound waves travel into the ear canal, they vibrate the tympanic membrane, commonly called the eardrum. The eardrum is a thin, cone-shaped piece of skin. It is positioned between the ear canal and the middle ear.
Before the sound passes on to the inner ear, the total pressure must be amplified.
This is the job of the ossicles, a group of tiny bones in the middle ear. The ossicles are actually the smallest bones in your body.
Next the cochlea in the inner ear conducts sound through a fluid, instead of through air.
The cochlea is by far the most complex part of the ear. Its job is to take the physical vibrations caused by the sound wave and translate them into electrical information the brain can recognize as distinct sound.
The organ of corti is a structure containing thousands of tiny hair cells. It lies on the surface of the basilar membrane and extends across the length of the cochlea.
When these hair cells are moved, they send an electrical impulse through the cochlear nerve. The cochlear nerve sends these impulses on to the cerebral cortex, where the brain interprets them.

There is no actual movement of air from the sound-producing body to our ear. The air layers only vibrate back and forth, and transfer the sound energy from one layer to the next layer till it reaches our ear. Example: If we turn on a gas tap for a few seconds, a person standing a few metres away will hear the sound of escaping gas first and the smell of gas reaches him afterwards. The sound of gas travels through the vibrations of air layers so it reaches first, but the smell of gas reaches the person through the actual movement of the air layers, which takes more time. So, it is clear that the sound is not being transmitted by the actual movement of air from the gas tap to person, otherwise he would hear and smell the gas at the same time.

A wave in which the particles of the medium vibrate back and forth in the 'same direction', in which the wave is moving, is called a longitudinal wave. These waves can be produced in all the three media: solids, liquids and gases.

A wave in which the particles of the medium vibrate up and down 'at right angles' to the direction in which the wave is moving, is called a transverse wave. It can be produced in solids and liquids but not in gases.