\(\cfrac { 1 }{ f } =\left( { \mu }_{ 21 }-1 \right) \left( \cfrac { 1 }{ { R }_{ 1 } } -\cfrac { 1 }{ { R }_{ 2 } } \right) \)

(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.

(i) No,
(ii) Yes, stopping potential increases with increases of frequency.

Peacock feathers get their iridescent coloration from light interacting with 2 dimensional photonic crystal structures just tens of nanometers thick.

The communication is the processing, sending and receiving of information with the help of a suitable communication system and transmission medium.

The moderator is a material used to convert fast neutrons into slow neutrons
(i) A billiard ball striking a stationary billiard ball of equal mass would itself be stopped but the same billiard ball bounces off almost with same speed when it strikes a heavier mass.
(ii) This is the reason for using lighter nuclei as moderators.

(i) The number of turns N.
(ii) The magnetic induction B.
(iii) The area of coil A.

(i) As the plate oscillate, the changing magnetic flux through the plate produces a strong eddy current in the direction, which opposes the cause.
(ii) Also copper being diamagnetic substance, it gets magnetised in the opposite direction, so the motion of copper plate is stopped.

emf = Terminal voltage + P.D. across internal resistance. E = V + Ir
A cell has always same internal resistance a part of the emf is consumed in doing wire against the internal resistance in a closed circuit. So, E > V (or) V < E.