Question

An object is kept at a distance of 1m from a lens of power +2D:

1. Identify the type of lens.
2. Calculate its focal length and distance of the image formed.

Answer 1

1. The given lens is convex because convex lenses have a positive power.
2. P = ${\displaystyle \frac{1}{\text{f}}}$

        +2 = ${\displaystyle \frac{1}{\text{f}}}$

       f = +0.50 m

Its focal length is +0.50 m.

Using the relation = ${\displaystyle \frac{1}{\text{f}}=\frac{1}{\text{v}}-\frac{1}{\text{u}}}$

${\displaystyle \frac{1}{\text{v}}=\frac{1}{\text{f}}+\frac{1}{\text{u}}}$

= ${\displaystyle \frac{1}{0.5}+\frac{-1}{1}}$

= ${\displaystyle \frac{2+(-1)}{1}}$

v = 1 m