(i) Fringe width of interference fringes is given by \(\beta =\cfrac { D\lambda }{ d } \propto \cfrac { 1 }{ d } \) When d is infinitely small, fringe width β will be too large.
(ii) In such a case even a single fringe may occupy the whole field of view. Hence, the interference pattern cannot be detected.

The middle point on the spherical surface of the mirror (or) the geometrical center of the mirror is called pole (P) of the mirror.

The resistance of the semiconductor changes in accordance with the radiant energy incident on it.

(I) In 1954, George Devol invented the first digitally operated programmable robot called Unimate. George Devol and Joseph Engelberger, the father of the modern robotics industry formed the world's first robot company in 1956.
(ii) In 1961, Unimate, was operated in a General Motors automobile factory for moving car parts around in New Jersey.

It is defined as the quantity of radiation which produces 1.6 x 10¹² pair of ions in 1 gram of air.

Microwaves are used. They are considered suitable for radar systems for aircraft navigation due to their short wavelength or high frequency. Its wavelength range 1 x 10^-3 m to 3 x 10^-1 m and frequency range is 3 x 10¹¹Hz to 1 x 10⁹ Hz.

The magnetic flux density can also be defined as the number of magnetic field lines crossing unit area kept normal to the direction of line of force. 
Its unit is Wb m^-2 or telsa.

The maximum current at series resonance is limited by the resistance of the circuit. For smaller resistance, a larger current with a sharper curve is obtained and vice versa.

Current produces thermal energy, thermal energy may also be suitably used to produce an electromotive force. This is known as thermoelectric effect.

(i) In polar molecules, the centers of the positive and negative charges are separated even in the absence of an external electric field.
(ii) They have a permanent dipole moment.
(iii) Examples : H₂O, N₂O, HCI and NH₃.