Question

A concave mirror of radius of curvature 10 cm is cut into two equal parts, slightly separated and placed in front of a monochromatic line source S of wavelength 2000 $\hat{A}$ as shown in figure. Consider only interference in reflected light after first reflection from mirrors. Assume direct light from S is blocked from reaching the screen

Assume A is the position of first order maxima on the screen. Now the point object is moved away from normal to screen with constant speed, then:

• A. fringe width will increase
• B. fringe width will decrease
• C. Intensity at point A on screen will continuously decrease
• D. Intensity at point A on screen will first increase, then decrease.

Answer 1

The correct option is A

fringe width will increase

At source is moved away from the mirror both images will move towards the mirrors ‘D’ will increase and ‘d’ will decrease.