Two identical glass rods `S_(1)` and `S_(2)` (refractive index=1.5) have one convex end of radius of curvature 10 cm. They are placed with the curved surfaces at a distance d as shown in the figure, with their axes (shown by the dashed line) aligned. When a point source of light P is placed inside rod `S_(1)` on its axis at a distance of 50 cm from the curved face, the light rays emenating from it are found to be parallel to the axis inside `S_(2)`. The distance d is

Options

A. 60 cm to the left of the system
B. 70 cm
C. 80 cm
D. 90 cm

Answer

B

Explanation

For first surface
`(1)/(V) - (1.5)/(-50) = (1 - 1.5)/(-10) implies V = 50 cm `
for second surfaces
`(1)/(oo) - (1)/(-(d - 50)) = (1.5 -1)/(10)`
d = 70 cm `" " therefore (B)`