A thin glass (refractive index 1.5) lens has optical power of - 5D in air. Its optical power in a liquid medium with refractive index 1.6 will be .....

Options

A. `-1D`
B. `1D`
C. `-5D `
D. `0.625D`

Answer

B, D

Explanation

`P_1=(1)/(f_1)=((n_2-n_1)/(n_1))((1)/(R_1)-(1)/(R_2))` for air
`P_2=(1)/(f_2)=((n_2-n_1)/(n_1))((1)/(R_1)-(1)/(R_2))` for liquid
`therefore(P_1)/(P_2)=((n_2-n_1)/(n_1))((n_1)/(n_2-n_1))`
`=((1.5-1.0)/(1))((1.6)/(1.5-1.6))`
`=0.5xx(-16)=-8`
`therefore(-5D)/(P_2)=-8`
`therefore P_2=5/8=0.625` D