Question

Light from a point source in air falls on a spherical glass surface whose radius of curvature and refractive index are $20 \,cm$ and $1.5$ respectively. If the distance of light source from the glass surface is $100 \,cm$, then at which position image will be formed?

• A. $25\,cm$
• B. $50\,cm$
• C. $100\,cm$
• D. $200\,cm$

Answer 1

Answer: (C)

Here, $\mu_1 = 1, R = 20 \,cm$,
$ u = -100\, cm, \mu_2 = 1.5$
$\therefore \frac{1}{100}+\frac{1.5}{v} = \frac{1.5-1}{20} = \frac{1}{40}$
or $\frac{3}{2\,v} = \frac{1}{40}-\frac{1}{100}$
$=\frac{5-2}{200} = \frac{3}{200}$
$\Rightarrow v= 100\,cm$
Hence, the image is formed at a distance of $100\, cm$ from the glass surface.