Question

A convex spherical refracting surfaces separates two media glass and air `(mu_g=1.5).` If the image is to be real, at what minimum distance u should the object be placed in air if R is the radius of curvature
A. `ugt3R`
B. `ugt2R`
C. `ult4R`
D. `ultR`

Answer 1

Correct Answer - B

`1.5/v-1.0/(-u)=(1.5-1.0)/(+R)`
or `1.5/v=(-1)/u+1/(2R)`
For image to real (for negative value of u) v should
be positive. Hence, `1/ult1/(2R) or ugt2R.`