Q: A far sighted person cannot focus distinctly on objects closer than 1 m. What is the power of lens that will permit him to read from a distance of 40 cm ?

Sol: As near point is 1m and distance of objects is 0.40 m

Both in front of lens.

$\large p = \frac{1}{f} = \frac{1}{v} – \frac{1}{u} $

$\large p = \frac{1}{f} = \frac{1}{-1} – \frac{1}{-0.40} $

p = 1.5 D