Question

Two coherent sources of intensity ratio $1:4$ produce an interference pattern. The fringe visibility will be

• A. 1
• B. 0.8
• C. 0.4
• D. 0.6

Answer 1

Answer: (B)

Fringe visibility $V=\frac{2\sqrt{I_1{I}_2}}{I_1+I_2}$
where $I_1$ and $I_2$ are intensities of coherent sources.
Given, $\frac{I_1}{I_2}=\frac{1}{4}$
$\therefore I_2=4I_1$
$\therefore$ Fringe visibility
$=\frac{2\sqrt{I_1\times 4I_1}}{\left(I_1\times 4I_1\right)}$
$=\frac{2\times 2I_1}{5I_1}=\frac{4}{5}$
$\Rightarrow V=0.8$