When mechanical waves have a frequency below the audible range, these are called

Rain drops acquire spherical shape due to 

If a sound travels from air to water, the quantity that remain unchanged is

The basic reason for the extraordinary sparkle of suitably cut diamond is that

Optical fiber works on the principle of

The thrust exerted by a body on a surface = ?

The law of definite proportions was stated by

Consider the following statements A simple pendulum is set into oscillation. Then 
(1) The acceleration is zero when the bob passes through the mean position. (2) In each cycle, the bob attains a given velocity twice. 
(3) Both acceleration and velocity of the bob are zero when it reaches its extreme position during the oscillation. 
(4) The amplitude of oscillation of the simple pendulum decreases with time. Which of these statements are right?

The min. number of geostationary satellites needed for uninterrupted global coverage is:

Vehicles use _____ to see the objects coming from behind.