Browse by Stream
QnA
Home
QnA
Go To Your Study Dashboard

Get Answers to all your Questions

header-bg qa
  • Home
  • Engineering
  • A convex lens is made of glass of refractive index 1.5 . If radius of curvature of each of its two surfaces is 20 cm, find the ratio of the power of the lens, when placed in air to its po

A convex lens is made of glass of refractive index 1.5 . If radius of curvature of each of its two surfaces is 20 cm, find the ratio of the power of the lens, when placed in air to its power, when immersed inside a liquid of refractive index 1.25 .

Option: 1

10


Option: 2

5


Option: 3

2.5


Option: 4

2


Answers (1)

best_answer

 

 

 

                                                                P_{Lens}=\frac{1}{f} \ \ \ and \ \ \ P_{Mirror} = \frac{-1}{f}  

 

 

\text { Here, } R_{1}=20 \mathrm{cm}=0.20 \mathrm{m} ; R_{2}=-20 \mathrm{cm}=-0.2 \mathrm{m}

\begin{array}{l}{\text {In the first case, When lens is placed in air: If } P_{1} \text { is power of the lens when }} \\ {\text { placed in air, so, }} \\ {\qquad \begin{aligned} P_{1} &=(\mu-1)\left(\frac{1}{R_{1}}+\frac{1}{R_{2}}\right)=(1.5-1)\left(\frac{1}{0.2}-\frac{1}{-0.2}\right) \\ &=0.5(5+5)=5 \mathrm{D} \end{aligned}}\end{array}

Now in the second case when lens is placed inside the liquid: If \mu' be the refractive index of the material of the lens w.r.t. the liquid. Then, power of the lens, when placed inside the liquid is given by

\\ \begin{array}{c}{P_{2}=\left(\mu^{\prime}-1\right)\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)} \\ \\ {\text { Here, } \quad \mu^{\prime}=\frac{\mu_{\text {glass }}}{\mu_{\text {liquid }}}=\frac{1.5}{1.25}=1.2} \\ \\ {\therefore \quad P_{2}=(1.2-1)\left(\frac{1}{0.2}-\frac{1}{-0.2}\right)=0.2(5+5)=2 \mathrm{D}} \\ \\ {\text { Hence, } \frac{P_{1}}{P_{2}}=\frac{5}{2}=2.5}\end{array}

 

 

Posted by

Gautam harsolia

View full answer

JEE Main high-scoring chapters and topics

Study 40% syllabus and score up to 100% marks in JEE

Similar Questions

Trending Articles/News

anam-khan

Telangana to offer free JEE, NEET, CLAT coaching to government school students
anam-khan

BTech 2025 Admission LIVE: JoSAA revised schedule out on josaa.nic.in; updates on MHT CET, KEAM counselling
anam-khan

Andhra launches free JEE, NEET coaching to over 1 lakh govt school students

Latest Question