Question

Why the center of Newton rings is dark?​

Answer 1

the point of contact Thè path different is zero but

one of inter ferying ray is reflected so the effective path difference become / 2 and in this condition minimum intensity is created at center so the center of Newton ring is dark

Answer 2

The point of contact the path difference is zero but one of the interfering ray is reflected so the effective path difference becomes λ/2 thus the condition of minimum intensity is created in the center.