PHYSICS [3 Mark Question Answer]

The speed of sound in a medium depends mainly upon the elasticity and the density of the medium. The speed of sound increases as the density of the medium increases. Since the density of solids is the maximum, followed by liquids and gases, sound travels fastest through solids, little slower through liquids and slowest through gases or air. The speed of sound also depends upon the pressure and speed of the fluid medium, temperature and humidity.

Sound Navigation And Ranging (SONAR) is an instrument that uses the concept of echo (or reflection of sound) to measure the depth of oceans. This instrument produces and transmits high frequency (ultrasonic) waves towards the seabed, from any point, say A on a ship/boat. After striking the seabed, these waves are reflected upward and received at another point, say B. The time elapsed between transmitting and receiving back these waves is recorded. Using the speed of sound in sea water as 1560 m/s at 20 °C, and the elapsed time, the depth of the seabed can easily be calculated.

An echo is defined as a repetition of sound produced by the reflection of sound waves from a reflecting surface.
Conditions required for occurrence of an echo are :

• The minimum distance between the source of sound and the reflecting surface is around 17 m.
• There is a high wall or a hill or a high-rise building, which can act as a reflecting surface.
• The sound is loud enough so that it reaches the receiver after reflection.