An object of diameter 6 cm is placed at a distance of 10 cm in front of a lens with a power of +5.0 D. The diameter of the image of the object will be:

Question

Question

This question was previously asked in

RRB Group D 17 Sept 2022 Shift 3 Official Paper

Answer 1

The correct answer is option 1)12cm

Given:

of a lens whose power is +5.0 D.

Formula:

Power of lens:

len formula:

Calculations:

\(P={1\over f}\)

\(f={1\over P}={1\over5}=0.2m=20cm\)

\({1\over f}={1\over v}-{1\over u}\)

\({1\over 20}={1\over v}-{1\over -10}\)

\({1\over v}={1\over 20}+{1\over -10}={1-2\over20}\)

\(v={-20\over 1}=-20cm\)

We know that, the magnification of the lens:

\(m={di\over do}={v\over u}\)

\({di\over 6}={-20\over -10}=2\)

\(di=6*2=12cm\)

Therefore, the diameter of the image is 12cm.