Question

The ratio of intensity at the centre of a bright fringe to the intensity at a point distant one fourth of the distance between two successive bright fringes will be

• A. 4
• B. 3
• C. 2
• D. 1

Answer 1

Answer: (C)

2

Answer 2

Intensity at the centre of bright fringe, $I_0 = I + I + 2 \sqrt{II} cos 0^\circ$ $I_0 = 2 I + 2 I$ $I_0 = 4 I$ Intensity at a point distant $\frac{\beta}{4}$ (with a phase diffrerence = $\frac{2 \pi}{4} = \frac{\pi}{2})$ is $I' = I + I + \sqrt{II} cos \frac{\pi}{2}$ $I' = 2 I \big[ \because \, cos \frac{\pi}{2} = 0 \big]$ $\therefore\frac{I_0}{I'} = \frac{4 I}{2 I} = 2$