Question

a converging lens of refractive index 1.5 is kept in a medium of same refractiveindex. what would be the focal length of lens in this medium?

Answer 1

Refractive index of the lens = 1.5 =Refractive index of medium 
the lens in a medium (liquid) will be act like a plane of glass.
 Its focal length will be infinte 
By using the formula of lens maker.

1/f = (u - 1) (1/R1 - 1/R2)

1/f = (u2/u1 -1) (1/R1 - 1/R2)
    u1 = u2
1/f = 0
thus, f = infinity 

Answer 2

Answer:

d

Explanation:

We have, Len's maker formula =  

f

1

​  

=(  

μ  

1

​  

 

μ  

2

​  

 

​  

−1)(  

R  

1

​  

 

1

​  

−  

R  

2

​  

 

1

​  

),

Here, μ  

1

​  

=μ  

2

​  

=1.5

⇒  

f

1

​  

=0

⇒f=∞