The intensity of light depends upon:

In the phenomenon of interference :-
$(a)$ Total energy is conserved
$(b)$ Total energy is not conserved
$(c)$ Only bright fringes are formed
$(d)$ The frequency of two sources is equal

$n$ incoherent sources, each emitting beams of intensity $I_0$, are superimposed at a point. The resultant intensity at the point is:

Two coherent waves of equal intensity produce a maximum intensity of $100$ units. If the intensity of one of the sources is reduced by $20\%$,then the new maximum intensity will be:

Two waves having intensity $I$ and $9I$ produce interference. If the resultant intensity at a point is $7I$,what is the phase difference between the two waves?........$^o$

Two coherent plane waves of identical frequency,polarization,and intensity $I$ interfere at a point where they differ in phase by $60^{\circ}$. What is the resulting intensity?