Question

Intensity of central bright fringe due to interference of two identical coherent monochromatic sources is $I$. If one of the source is switched off, then intensity of central bright fringe becomes:

• A. $\frac{I}{2}$
• B. $\frac{I}{3}$
• C. $\frac{I}{4}$
• D. $I$

Answer 1

Answer: (C)

If each of the sources is producing an intensity $I$’ at the point of intereference then at the central maximum, intensity will be due to constructive interference of the light due to these two sources which will be 4I' and this is given as I, thus we have
$I^{\prime}=\frac{I}{4}$