First slide

Ray optics

Question

An equiconvex lens of focal length 10cm (at t=0) and refractive index (1.5) is placed in a medium whose refractive index varies with time as $μ = (1 + \frac{t}{10});$ t in seconds. The value of t when the lens acts as a diverging lens of focal length 20cm is

Easy

A

5 secs
B

10 secs
C

20 secs
D

25 secs

Solution

$- \frac{1}{20} = (\frac{1.5}{μ} - 1) (\frac{2}{R}) a n d \frac{1}{10} = (1.5 - 1) (\frac{2}{R}) = \frac{1}{R} \Rightarrow ∴ R = 10 c m$
$S o, μ = 2$
$∴ t = 10 \sec s$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App