If the velocity of sound is 3 m/s and the distance between the object is 3 m, find the time taken to hear an echo?

Sounds which are unpleasant to hear are called ________.

• A pleasant sound is called music.

Decreasing amplitude decreases _______.

Amplitude is denoted by  __________.

An increase in amplitude makes a sound wave _______.

Sounds that are pleasant to hear are called ultrasounds.

Ultrasounds are high frequency sounds.

Communication in the submarines is using infra waves.

The device that transmits ultrasounds in SONAR is called _______.

• A receiver receives the sound reflected from the depths of the sea and perceives it. 

Sound cannot travel through _________.

Echo is _________ of the sound.

• Refraction is the bending of sound waves when they enter from one medium to another medium.

The reflection of sound in a closed surface is called _______.

• Amplification refers to the increase of the amplitude or loudness of sound.
• The repetition of a sound that is caused by the reflection of sound wave in large spaces is called an echo.

Which of the below is used to amplify sound?

Units to measure sound:

• The unit of power is watt.
• The unit of force is newton.
• The unit of work is Joule.

SONAR is used in _______

A sonar can detect the enemy ship using
_________ .

Distance can be measured in___________.

• The SI unit of time is Second.
• The SI unit of pressure is Pascal.
• The SI unit of force is Newton.