A lens has a power of 10 D, when placed in air. When it is immersed in water `(mu =(4)/(3))` the change in power is (refractive index of lens material is 1.5)

Options

A. 2.55 D
B. 5.0 D
C. `+7.5 D `
D. `6.67 D `

Answer

D

Explanation

`P _(air) =(1)/(f_(air))`
`P _(water) =(mu_("water"))/(f_("water"))impliesP_("water")= (4//3)/(4f _("ari"))=(P _(air))/(3)impliesP_("water")`
`=3.33D`
Change is power `=100-3.33D = 6.67D`