Science Que-Ans (Each of 3 Mark )

The loudness depends on energy per unit area of the wave and on the response of the ear but intensity depends only on the energy per unit area of the wave and is independent of the response of the ear.

We hear more clearly in a room with curtains than in a room without curtains because curtains are bad reflectors of sound. They absorb most of the sound falling on them, and hence do not produce echoes. On the other hand, in rooms without curtains, there is a greater reflection of sound due to which some echoes are produced. These echoes cause a hindrance to hearing.

In most of the cases, a sound producing object vibrates so fast that we cannot see its vibrations with our eyes. The time interval between two successive vibration is lower than the persistence of vision. Hence we see the object in static state and not in vibration mode.

The outer ear is called pinna. It collects the sound from the surroundings. The collected sound passes through the auditory canal. At the end of the auditory canal there is a thin membrane called the eardrum or the tympanic membrane. When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates. The vibrations are amplified several times by three bones (the hammer, anvil and stirrup) in the middle ear. The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear. In the inner ear, the pressure variations are turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve and the brain interprets them as sound.

Sound can be produced by the following methods:

1. By vibrating strings (as in a sitar).
2. By vibrating air (as in a flute).
3. By vibrating membranes (as in a drum).
4. By vibrating plates (as in cymbals).

When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heard through the air. This is due to the fact that sound travels much more fast through the railway line made of steel than through air.

Ultrasound waves are made to pass through one face of the metal block and ultrasound detectors are placed on the opposite face of the block to detect the transmitted ultrasound waves.

1. If the ultrasound waves pass uninterrupted through all parts of the metal block, then the block is flawless.
2. However, if the ultrasound waves are not able to pass through a part of the metal block and get reflected back, then there is a flaw in the metal block.

Longitudinal waves have compressions and rarefactions. Compression: A compression is a region in a longitudinal wave where the particles are closest together. Rarefaction: A rarefaction is a region in a longitudinal wave where the particles are furthest apart.

If the air is gradually pumped out of the glass vessel, no sound of the electric bell can be heard because vacuum is created in the vessel and there are no air molecules to carry sound vibrations.

Bats emit high frequency ultrasonic squeaks while flying and listen to the echoes produced by the reflection of their squeaks from their prey. From the time taken by the echo to be heard, bats can judge the distance of the prey in their path and catch it.

Sound cannot be heard on the surface of moon because there is no air on the moon to carry the sound waves. Astronauts talk to one another on the surface of moon through wireless sets using radio waves. This is because radio waves can travel even through vacuum though sound waves cannot travel through vacuum.

1. Echolocation: Echolocation is the method used by some animals to locate the objects by hearing the echoes of their ultrasonic squeaks.
2. Echocardiography: Echocardiography is the use of ultrasound waves to investigate the action of the heart.
3. Ultra sonography: Ultra sonography is the technique of obtaining pictures of internal organs of the body by using echoes of ultrasound pulses.

Crest: The 'elevation' or 'hump' in a transverse wave is called crest. It is that part of the transverse wave which is above the line of zero disturbance of the medium. Trough: The 'depression' or 'hollow' in a transverse wave is called trough. It is that part of the transverse wave which is below the line of zero disturbance of medium. A transverse wave consists of crests and troughs.

Bats are able to fly at night without colliding with other objects because they emit high frequency ultrasonic squeaks while flying and listen to the echoes produced by the reflection of their squeaks from the objects or obstacles in their path. From the time taken by the echo to be heard, bats can judge the distance of the object in their path and avoid it by changing the direction.

A light ray is a stream of light with the smallest possible cross-sectional area. (Rays are theoretical constructs.) The incident ray is defined as a ray approaching a surface. The point of incidence is where the incident ray strikes a surface. The normal is a construction line drawn perpendicular to the surface at the point of incidence. The reflected ray is the portion of the incident ray that leaves the surface at the point of incidence. The angle of incidence is the angle between the incident ray and the normal. The angle of reflection is the angle between the normal and the reflected ray.The Laws of reflection:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, the normal, and the reflected ray are coplanar.

Specular reflection (regular reflection) occurs when incident parallel rays are also reflected parallel from a smooth surface. If the surface is rough (on a microscopic level), parallel incident rays are no longer parallel when reflected. This results in diffuse reflection (irregular reflection). The laws of reflection apply to diffuse reflection. The irregular surface can be considered to be made up of a large number of small planar reflecting surfaces positioned at slightly different angles. Indirect (or diffuse) lighting produces soft shadows. It produces less eye strain than harsher, direct lighting. The applet below illustrates how reflection and refraction takes place in common substances such as water, vacuum, air, glass, and even diamond.

Yes, sound follow the same laws of reflection as light does. In case of light, the angle of incident light is equal to angle of reflection of light. In case of sound, the incident wave , the reflection wave and normal to a point of incidence all lie in the same plane. To observe the reflection of sound, take a drawing board and fix it on the floor. Put two metallic or cardboard tubes as shown in Fig. These tubes are making some angle with each other. Put a clock near the end of one tube and a screen between the two tubes so that sound of clock may not be heard directly. The sound (like tick-tick) waves pass through the tube are reflected by the drawing board. The reflected sound waves enter the second tube and are heard by the ear placed in front of the second tube

Sound is produced by the following objects:

1. Vibrating stretched strings of sitar.
2. Vibrating stretched membranes of tabla.
3. Vibrating prongs of a tuning fork.
4. Vibrating wings of mosquito.
5. Vibrating air columns in flute.

Wavelength is the distance between two consecutive compressions or two consecutive rarefactions. Time period is the time taken to travel the distance between any two consecutive compressions or rarefactions from a fixed point.

• Wavelength: The distance between two consecutive compressions or two consecutive rarefactions is known as the wavelength. Its SI unit is metre (m).
• Frequency: The number of complete oscillations per second is known as the frequency of a sound wave. It is measured in hertz (Hz).
• Amplitude: The maximum height reached by the crest or trough of a sound wave is called its amplitude.

Applications of ultrasound are:

1. Ultrasound is used in industry for detecting flaws in metal blocks without damaging them.
2. In hospitals, ultrasounds are used to investigate the internal organs of the human body such as liver, kidneys, uterus, etc.
3. Ultrasounds are also used to monitor the growth of fetus inside the mother’s uterus.