Maxima : A point having maximum intensity is called a maxima. 'I' is maximum if

A point will be a maximum if two waves reaching there have a path difference of even multiple of 'λ'/2

I_max = K 4a² × 1 = 4 Ka²

Intensity 'i' due to a single source,

i= ka²

I_max = 4i

Minima : A point having minimum intensity is called a minima. 'I' is minimum if

A point will be a minima if the two waves reaching that point have a path difference equal to the odd multiple of 'λ'/2.

I_min = K .4a² × 0 = 0.

Thus, the screen is divided into regions having intensity 4i and zero.

It appears that the light energy (= 2i) from the minima region has been removed to the maxima region making total intensity '2i + 2i = 4i' at the place.Thus, it is a case of redistribution of energy and not disappearance of energy at minima.This is in accordance with the law of conservation of energy according to which energy can neither be created nor destroyed.