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

The correct option is C 100 cm

Here, ${\mu }_2=1.5,{\mu }_1=1,R=20cm$

$u=-100cm,v=?$

As light goes from air (rarer medium) to glass (denser medium), therefore,

$-\frac{{\mu }_1}{u}+\frac{{\mu }_2}{v}=\frac{{\mu }_2-{\mu }_1}{R}$

$-\frac{1}{100}+\frac{1.5}{v}=\frac{1.5-1}{20}=\frac{1}{40}$

$\frac{3}{2v}=\frac{1}{40}-\frac{1}{100}=\frac{5-2}{200}=\frac{3}{200}=100cm$

$\therefore$ The image is formed at a distance of $100cm$ from the glass surface, in the direction of incident light.