Calculate the area of disk of radius 'a' using integration
Concept Questions :-
A disk of radius a can be assumed to be made of infinite concentric rings each of small thickness dr. Now consider a ring of inner radius r and outer radius r+dr. If we cut out this smalll ring, cut it along the radius and straighten it out, we obtain a rectangle of length and thickness dr.
Total area of disk [Since radius of innermost ring is zero and that of outer most is a]