P is power of a lens. Whats is the expression of findinfg P in a medium. Is it  1/f or n_med/f_med. Please tell

 i am not sure but i think it is

I m sure

The power of lens is defined as     P =   1 / f



where 'f' must be expressed in metres. S.I. unit is m^-1 also known as Dioptre (D).

Question:

Whats is the expression of findinfg P in a medium. Is it  1/f or n_med/f_med. Please tell

1/f = (n-1)(1/r₁ - 1/r₂)

here n = ratio of refractive index of lens material and medium in which the lens is kept

                n_lens / n_medium

r₁ and r₂ are radius of curvatures. (r₁ and r₂ follow sign conventions)

power of a lens is i/f and if it is n mediam /f then    n medium say glass is 1.5 thereforeformula becomes 1.5/f which is wrong i think      so 1/f is right answer

It is n_med/f_med

I verified with my professor.

Peace