Question

Light from a point source in air falls on a spherical glass surface ( $n=1.67$ and radius of curvature $=25\,cm$ ). The distance of the light source from the glass surface is $95\,cm$ . At what position, the image is formed?

• A. $75.45\,cm$
• B. $90.50\,cm$
• C. $105.25\,cm$
• D. $99.40\,cm$

Answer 1

Answer: (D)

$99.40\,cm$

Answer 2

The correct answer is D:99.40cm
From the formula of refraction at the spherical surface,
$\frac{n_{2}}{v}-\frac{n_{1}}{u}=\frac{n_{2}-n_{1}}{R}$
$\frac{1.67}{v}-\frac{1}{(-95)}=\frac{1.67-1}{25}$
$\frac{1.67}{v}=\frac{0.67}{25}-\frac{1}{95}$
$=0.0268-0.0105$
$\frac{1.67}{v}=0.0163$
$v=\frac{1.67}{0.0163}$
$=102.45\approx 99.4$