Ray Optics Question 8
Question 8 - 30 January - Shift 1
A person has been using spectacles of power-1.0 diopter for distant vision and a separate reading glass of power 2.0 diopters. What is the least distance of distinct vision for this person:
(1) $10 cm$
(2) $40 cm$
(3) $30 cm$
(4) $50 cm$
Show Answer
Answer: (4)
Solution:
Formula: Lens Maker’s Formula
$ \begin{aligned} & \frac{1}{V}-\frac{1}{u}=\frac{1}{f} \\ & P=2 D=2 m^{-1} \end{aligned} $
$ \begin{aligned} & \Rightarrow \frac{1}{f}=\frac{2}{100} cm^{-1} \\ & \frac{1}{V}-(-\frac{1}{25})=\frac{2}{100} \\ & \Rightarrow \frac{1}{V}=\frac{1}{50}-\frac{1}{25} \end{aligned} $
$\Rightarrow V=-50 cm$
