Question

A thin equi-convex lens is made of glass with refractive index 1.5, and its focal length is 0.2 m. If it acts as a concave lens of 0.5 m focal length when dipped in a liquid, the refractive index of the liquid is:

Answer 1

Answer:

Explanation:

Apply this formula .

ng -1 / ( ng/nl)-1 = multiple on f of glass lens

i.e this multiple× fg = foc

Of lens dipped in liquid

Here, nl=refractive index of liquid

So 1.5-1 / (1.5/nl)-1= multiple on 0.2m

Now, multiple on 0.2m is , 0.5/0.2=5/2

So,

0.5 / (1.5/nl)-1 = 5/2

(7.5/nl )-5= 1

7.5= 6nl

nl=7.5/6

=1.25

Ans=1.25