Question

For a change in elevation level of $1.5\mu \text{m}$ between an optical flat and a surface, a light wave of wavelength $0.5\mu \text{m}$ produces fringes. The number of fringes is

• A. 9
• B. 6
• C. 3
• D. 12

Answer 1

The correct option is B 6

$2\left(\Delta x\right)=n\lambda$
$\therefore 2\times (1.5\times {10}^{-6})=n\times 0.5\times {10}^{-6}$
$\therefore n=\frac{2\times 1.5\times {10}^{-6}}{0.5\times {10}^{-6}}=6\text{fringes}$