Question

A convex refracting spherical glass surface has a radius of curvature $20cm$ and refractive index of $1.5$ . A ray of light coming from a source located at $100cm$ from the glass surface strikes it. The position of the image will be formed at:

• A. $25cm$ , on opposite side of source
• B. $50cm$ , on same side of source
• C. $100cm$ , on opposite side of source
• D. $200cm$ , on same side of source

Answer 1

Answer: (C)

Here, ${\mu }_1=1,R=20cm,u=-100cm,{\mu }_2=1.5$
$\therefore \frac{1}{100}+\frac{1.5}{v}=\frac{1.5-1}{20}=\frac{1}{4}$
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.