A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What

The power (P) of a lens of focal length f is given by the relation 

\( Power\,(P)=\frac{1}{f}\)

(i) Power of the lens (used for correcting distant vision) = -5.5 D

Focal length of the lens (f) =\( \frac{1}{p}\)

\( f=\frac{1}{-5.5}\)

\( f =-0.181 m\)

The focal length of the lens (for correcting distant vision) is - 0.181 m.

(ii) Power of the lens (used for correcting near vision) = +1.5 D

Focal length of the required lens (f) = \( \frac{1}{p}\)

\( f=\frac{1}{1.5}=+0.667 \,m\)

The focal length of the lens (for correcting near version) is 0.667 m.