Question

When a film is illuminated by white light, its upper portion appears dark, Path difference between two reflected beams at the spot must be

• A. zero
• B. $\lambda$/2
• C. 2$\lambda$/2
• D. $\pi$

Answer 1

Answer: (B)

$\lambda$/2

For dark band, path difference $x=(2N-1)\frac{\lambda }{2}......N=1,2,...$

$\therefore x=\frac{\lambda }{2},\frac{3\lambda }{2},\frac{5\lambda }{2},......$