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)

100 cm

Answer 2

: since light goes from air (rarer medium) to glass (denser medium),

$\therefore - \frac { \mu _ { 1 } } { \mathrm { u } } + \frac { \mu _ { 2 } } { \mathrm { v } } = \frac { \mu _ { 2 } - \mu _ { 1 } } { \mathrm { R } }$

Here, $\mu _ { 1 } = 1 , \mathrm { R } = 20 \mathrm {~cm} , \mathrm { u } = - 100 \mathrm {~cm} , \mu _ { 2 } = 1.5$

or

v = 100 cm

Hence, the image is formed at a distance of 100 cm from the glass surface.