Find the focal length of a lens of power `- 2.0 D`. What type of lens is this ?

Explanation

The power of this lens has a negative sign (or minus sign), so this is a concave lens. Now,
`"Power, "P=1/(f("in metres"))" "(f="focal length")`
`"So, "-2.0 = 1/f`
`"And, "f= -1/2.0 m`
`"Or "f = - 1/(2.0)xx100 cm`
So, Focal length of lens, f = - 50 cm