Question

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

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

Answer 1

Answer: (C)

Here, ${\mu }_1=1,R=20cm$,
$u=-100cm,{\mu }_2=1.5$
$\therefore \frac{1}{100}+\frac{1.5}{v}=\frac{1.5-1}{20}=\frac{1}{40}$
or $\frac{3}{2v}=\frac{1}{40}-\frac{1}{100}$
$=\frac{5-2}{200}=\frac{3}{200}$
$\Rightarrow v=100cm$
Hence, the image is formed at a distance of $100cm$ from the glass surface.