Question

Focal length of a convex lense in air is `10cm`. Find its focal
length in water. Given that `mu_g=3//2` and `mu_w=4//3`.

Answer 1

Correct Answer - C::D
`(1)/(f_("air"))=(mu_g-1)(1/R_1-1/R_2)`……(i)
and `(1)/(f_("water"))=(mu_g/mu_w-1)(1/R_1-1/R_2)`……(ii)
Dividing Eq. (i) by Eq. (ii), we get
`(f_("water"))/(f_("air")) = ((mu_(g)-1))/((mu_(g)//mu_(w)-1))`
Substituting the values, we have
`(f_("water"))/(f_("air"))=((3//2-1))/(((3//2)/(4//3)-1))f_("air")`
`=4f_("air")=4xx10=40cm`