Question

Light from a point source in air falls on a spherical glass surface (n = 1.5, radius of curvature = 10cm). The distance of the light source from the glass surface is 50 cm. The position at which the image is formed is:

• A. 100 cm in air
• B. 150 cm in glass
• C. 200 cm in air
• D. 50 cm in glass

Answer 1

Answer: (B)

150 cm in glass

Answer 2

$\text{ We use the lens-maker's formula:}$
$\frac{n_1}{s} + \frac{n_2}{s'} = \frac{n_2 - n_1}{R}$
$\text{Substitute } n_1 = 1, \, n_2 = 1.5, \, R = 10 \, \text{cm}, \text{ and } s = 50 \, \text{cm}. \text{ Solving this gives } s' = 150 \, \text{cm}.$