Question

Rohit placed a pencil perpendicular to principal axis in front of a converging lens of focal length 30cm. The image formed is three times enlarged than the size of the pencil. Calculate the two possible distances of the object from the mirror.

Answer 1

here is your answer on the image.

Answer 2

We know that, Magnification 

\(m=\frac{-v}{u}\)

\(2=\frac{-v}{u}\)

v = -2u

Using the mirror formula

\(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)

\(\frac{1}{-2u}+\frac{1}{u}=\frac{1}{-30}\)

\(\frac{-1+2}{2u}=\frac{-1}{30}\)

\(\frac{1}{2u}=\frac{-1}{30}\)

\(\frac{-30}{2}-u\)

u = -15 cm/s