Q 12-09-001JEE MainTop questionMedium
An object is placed $30\ \text{cm}$ in front of a convex lens of focal length $20\ \text{cm}$. The image formed is
Answer: (A) $60\ \text{cm}$ behind the lens, real, magnified
Using $\frac1v - \frac1u = \frac1f$ with $u = -30\ \text{cm}$, $f = +20\ \text{cm}$:
$$\frac1v = \frac1{20} - \frac1{30} = \frac1{60} \;\Rightarrow\; v = +60\ \text{cm}$$
Positive $v$ means a real image on the other side; $m = v/u = -2$, so it is inverted and twice the size.
Solution by Sreeraj P, M.Sc Physics