Question

Two slits are made one millimetre apart and the screen is placed one metre away. What is the fringe separation when bluegreen light of wavelength $500\text{nm}$ is used?

• A. $0.5\text{mm}$
• B. $5\text{mm}$
• C. $50\text{mm}$
• D. $0.5\text{m}$

Answer 1

The correct option is A $0.5\text{mm}$

Given,
$d=1\text{mm}={10}^{-3}\text{m}$
$D=1\text{m}$
$\lambda =500\text{nm}=5\times {10}^{-7}\text{m}$
Therefore, fringe seperation is given by
$\beta =\frac{\lambda D}{d}=\frac{5\times {10}^{-7}\times 1}{{10}^{-3}}=0.5\text{mm}$