Science Question Answer (2 Marks)

We should not put a pin or pencil or any other sharp pointed objects in our ears because they can damage the ear-drum and damaging of ear drum can make us deaf.

Sound is produced when an object vibrates. For example, the sound of our voice is produced by the vibrations of two vocal cords in our throat caused by air coming from the lungs.

The sound of a 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.

Due to the very high speed of light we see the ball hitting the bat first. And it is due to comparatively lower speed of sound that the sound of hitting is heard a little later.

Vacuum means empty space, region with no matter particles. Sound cannot travel through vacuum because vacuum has no molecules which can vibrate and carry sound waves.

Reflection of sound: The bouncing back of sound when it strikes a hard surface is called reflection of sound. Hard, solid surfaces are the best for reflecting sound waves.

Reverberation: The persistence of sound in a big hall due to repeated reflections from the walls, ceiling and floor of the hall is called reverberation.
If the reverberation time in a big hall is too long, then the sound becomes blurred, distorted and confusing due to overlapping.

Stethoscope: Stethoscope is a medical instrument used by the doctors for listening to the sounds produced within the human body, mainly in the heart and lungs.
Principle: It works on the principle of multiple reflections of sound.

Metal sheet, hard wood are good reflectors of sound.

A megaphone is a large, cone-shaped (or funnel-shaped) device for amplifying and directing the voice of a person who speaks into it. A megaphone works on the principle of multiple reflections of sound.

Echo: The repetition of sound caused by the reflection of sound waves is called echo. An echo is produced when sound is reflected from a hard surface such as a tall brick wall or a cliff.

SONAR: SONAR stands for Sound Navigation And Ranging.
Use: A sonar is an apparatus (or device) which is used to find the depth of a sea or to locate the underwater things like shoals of fish, shipwrecks and enemy submarines.

Sound: Sound is that form of energy which makes us hear. Sound waves are longitudinal waves in air.

The laws of reflection of sound are:

1. The incident sound wave, the reflected sound wave, and the normal at the point of incidence, all lie in the same plane.
2. The angle of reflection of sound is always equal to the angle of incidence of sound.

Quality (or timbre) is that characteristic of the sound by which we can distinguish between sounds of same pitch and loudness produced by different musical instruments (and different singers). The quality (or timbre) depends on the shape of the sound wave (or waveform) produced by it.

Pitch: Pitch is that characteristic of the sound by which we can distinguish between different of same loudness. It depends on the frequency of the sound waves.

Loudness: The loudness of sound is a measure of the sound energy reaching the ear per second. It depends on the amplitude of the sound waves.

An echo is heard sooner on a hot day because the speed of sound in air increases with temperature. So the speed of sound in air is more on a hot day, and an echo is heard sooner.

This is due to the fact that when the ringing bell is held tightly with our hand, it stops vibrating and the sound coming from it also stops.

When we strike a table lightly, then due to less energy supplied, the table top vibrates with a small amplitude and hence a soft sound is produced. However if we hit the table hard, due to greater energy supplied, the table top vibrates with a large amplitude and hence a loud sound is produced.

The cilings of halls are made curved so that sound, after reflection from the ceiling reaches all part of the hall.

Bulb horn: A bulb horn is a cone shaped wind instrument which used for signaling in bicycles, cars, buses, trucks and boats, etc.
Principle: A bulb horn works on the principle of multiple reflections of sound.

Infrasonic waves	Ultrasonic waves
These include of frequencies below 20Hz.	These include sounds of frequencies above 20,000Hz.
These sounds are produced by objects vibrating very slowly.	These sounds are produced by objects vibrating very rapidly.

We can conclude that wave B is louder than wave A as loundness of sound is directly proportional to the amplitude of the wave.

Infrasonic waves: Infrasonic waves include sounds of frequencies below 20Hz. These sounds are produced by objects vibrating very slowly.
Whales and elephants can produce these sounds.

Use of ultrasound in industry: Ultrasound is used in industry for detecting flaws in metal blocks without damaging them.
Use of ultrasound in hospital: In hospitals, ultrasound is used to investigate the internal organs of the human body such as liver, kidneys, uterus, etc.

Sound is a longitudinal wave that requires material medium for its propagation. Therefore, all the material mediums mentioned can be used as medium for the propagation of sound waves.

A ringing bell suspended in a vacuum chamber cannot be heard outside because sound cannot travel through vacuum as it has no molecules which can vibrate and carry sound waves.

Ultrasonic waves: Ultrasonic waves include sounds of frequencies above 20,000Hz. These sounds are produced by objects vibrating very rapidly.
Bats and dolphins can produce these sounds.