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)

Intensity at the centre of bright fringe, $I_0=I+I+2\sqrt{II}\cos 0^o$ $I_0=2I+2I$ $I_0=4I$ Intensity at a point distant $\beta /4$ (with a phase difference $=2\pi /4=\pi /2$ ) is $I=I+I+2\sqrt{II}\cos \frac{\pi }{2}$ $I=2I+2\sqrt{II}\times 0$ $I=2I$ $\therefore$ $\frac{I_0}{I}=\frac{4I}{2I}=2$