A thin made of glass of refractive index `1.5` has a front surface `+11 D` power and back surface `-6D` . If this lens is submerged in a liquid of refractive index `1.6`, the resulting power of the lens is

Options

A. `-0.5 D`
B. `+0.5 D`
C. `-0.625 D`
D. `+0.625D`

Answer

C

Explanation

Total power`P=P_(1)+P_(2)=11-6=5D`
Also `(f_(1))/(f_(a))=((._(a)mu_(g)-1))/((._(I)mu_(g)-1))implies(P_(a))/(P_(I))=((._(a)mu_(g)-1))/((._(I)mu_(g)-1))`
`implies(5)/(P_(I))=((1.5-1))/((1.5//1.6-1))impliesP_(I)=-0.625D`