Sound frequencies higher than 20,000 Hz are called ultrasound. It is used as diagnostic tool in medical science. It is also used to relieve pains in joints, muscles. It is used to detect flaws in metal and structures, and to test the thickness of various parts.

Sound needs a medium for propagation. Take a metal or glass tumbler. Place a cellphone in it. Ask your friend to give a ring on this cellphone. Listen to the ring carefully. Now surround the rim of the tumbler with your hands. Suck all the air of the tumbler. Once again make a ring in cellphone. Sound will completely stop because air has been removed completely from the vessel and forms vacuum. Hence sound needs a medium for propagation.

The frequency determines the shrillness or pitch of a sound. A drum vibrates with low frequency. Therefore, it produces low pitched sound. Whistle has a high frequency and therefore, produces a sound of higher pitch.

The vocal cords in men are about 20 mm long. In women these are about 5 mm shorter. Children have very short vocal cords. This is the reason why the voices of men, women and children are different.

We can differentiate sounds on the basis of their amplitude and frequencies.

Yes, as the sound of children is shriller than the sound of adults. So, the frequency of sound produced by a child is more than that of an adult.

Yes, the vocal cords vibrate to produce sound.

There is no atmosphere on the moon and sound waves need a medium to travel, so we cannot hear the sound on the moon.

Pitch is that characteristic of sound due to which distinction can be done between two sounds.

T = 0.025 s,
\(v=\frac { 1 }{ T } =\frac { 1 }{ 0.025 } =40Hz\)

Ultrasound refers to sound that has a frequency above the audible range (20,000 Hz) of the human ear.

Pitch is perceptual to sensation. Frequency is a physical quantity that can be measured.

Voice chord.

The hearing aid amplifies the sound sent from the surroundings.

Temporary deafness is an ill effect of noise pollution.