NOT gate is also called:

Sound can travel only in presence of

Optical centre is represented by

For a concave lens, the parallel rays appear to come from a. point behind the lens is called;

At room temperature, electrons cannot escape the metal surface due to ………….. of atomic nucleus:

The 1st practical electric battery is known as:

Loudness of sound depends on

In lens number ·of curved surfaces at least;

Lenses are used in optical devices;

The technique or method used to absorb undesirable sounds by soft and porous surface is called:

Frequency of silent whistle Lies between ___________

Characteristic by which We can distinguishbetween two sounds of same loudness and pitch is called