Question

Refraction takes place at a convex spherical boundary separating air-glass medium. For the image to be real, the object distance $({\mu }_g=\frac{3}{2})$

• A. should be greater than three times the radius of curvature of the refracting surface
• B. should be greater than two times the radius of curvature of the refracting surface
• C. should be greater than the radius of curvature of the refracting surface
• D. is independent of the radius of curvature of the refracting surface

Answer 1

The correct option is A should be greater than three times the radius of curvature of the refracting surface



Applying $\frac{{\mu }_2}{v}-\frac{{\mu }_1}{u}=\frac{{\mu }_2-{\mu }_1}{R}$
$\frac{1}{v}-\frac{1.5}{-u}=\frac{1-\left(1.5\right)}{-R}$
or $\frac{1}{v}+\frac{3}{2u}=\frac{1}{2R}$
For v to be positive $\frac{1}{2R}>\frac{3}{2u}$
or $u>3R$