PHYSICS [2 Mark Question Answer]

Cork will move up and down about the mean position at the same position along horizontal. It tells as that only the disturbance/energy is transferred from one particle to the other but particles of the medium do not move from one position to the other.

Bats make a series of twittering sound, so high pitched that human ear can not hear. These sound waves strike against the obstacles less in their path of flight and send back echoes to the bat’s ear. The echoes tell the bats, how they must turn in the air to avoid colliding with the obstacles or with one another.

Sound can not travel through vacuum. There is no material medium in the space for propagation of sound. Hence astronauts talk to each other through radio telephone in space. In radio telephone, message of one astronauts reach to the other with the help of radio waves, which can travel through vacuum.

A special whistle which can produce ultra sound, not heard by humans, is called Galton’s whistle. It is used to train dogs because they can hear ultrasounds upto a frequency of 40000 hertz.

Bats produce ultra sound which returns after striking an obstacle in their way. By hearing the reflected round, bats can judge the distance and direction of obstacle/prey in their way and hence bats can catch their prey during flight.

(a) Ultrasonic vibrations :Those vibrations, whose frequency is more than 20000 hertz and are not perceived by human ear, are known as ultrasonic vibrations.
(b) Dogs, bats and dolphins can hear ultrasonic vibrations.