VITEEE 2010 Paper

By using lens maker's formula,

1

f

=(µ−1)(

1

R1

−

1

R2

)
⇒5=(1.5−1)(

2

R

)...(i)
If a lens of refractive index µg is immersed in a liquid of refractive index µ1, then its focal length in liquid

1

f1

=(lµg−1)(

1

R1

−

1

R2

)
⇒−1=(

1.5

n

−1)(

2

R

)...(ii)
Dividing, (i) by (ii)
−5=

0.5n

1.5−n

⇒−7.5+5n=0.5n
⇒−7.5=−4.5n
⇒n=

75

45

=

5

3