Question Discussion & Solution

CONCEPT:

• Ultrasonic waves are the sound waves with frequencies higher than the upper audible limit of human hearing.
  • They have a short wavelength.
• Echo: If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
  • Echoes are heard due to the phenomenon of Reflection of sound waves.
• SONAR: It a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water
  • SONAR stands for ‘Sound Navigation and Ranging.’
  • SONAR is based on the principle of echo.
  • Sonar is often used as a measurement of acoustic location and echo characteristics of the target object in the water.
  • It sends ultrasonic waves towards the bottom area of the sea and after reflection, the sound comes to the ship. We measure the time taken by the sound wave and then we get the depth. 

EXPLANATION:​

• From the above discussion, we can say that the SONAR uses the principle of reflection of sound waves(Echo) to detect and locate objects. So option 2 is correct.
• Reverberation: The persistence of sound in a closed enclosure, due to continuous reflections at the walls or the floor or the ceiling of the enclosure, even after the source has stopped producing sound is known as 'reverberation'.

Rickshaw, bus and train are the means of transport.

Mobile and radio are the means of communication, so out of the given options only letter is a mean of communication.

There are 4 library functions provided by C defined under header file to facilitate dynamic memory allocation in C programming. They are:

• malloc()
• calloc()
• free()
• realloc()

49 ÷ 7 = 7,

70 ÷ 7 = 10,

91 ÷ 7 = 13,

99 ÷ 7 = 14.14

So, 49, 70 and 91 are the multiples of 7 while 99 is not a multiple of 7.

All are mammal except Lizard.