Radius of curvature of a concave spherical surface separating air-glass medium is R. A point object is placed on the principal axis in the glass `(m_(g) = 1.5)`. For the image to be real seen by

observer in air, distance of the object from P should be

Options

A. `2 R lt u lt 3 R`
B. `u lt 2R`
C. `u = R`
D. `u gt 3R`

Answer

D

Explanation

`(mu_(2))/(v) - (mu_(1))/(v) = (mu_(2) - mu_(1))/(1)`
`(1)/(v) - (1.5)/(-u) = (1 - 1.5)/(R )`
for v to be `+ve, (1)/(2R) - (3)/(2u) gt 0` or `u gt 3R`