Question

A student focussed the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle screen and the lens as under :

Position of candle $=12.0cm$
Position of convex lens $=50.0cm$
Position of the screen $=88.0cm$

What will be the nature of the image formed if he further shifts the candle towards the lens?

• A. Virtual and erect
• B. Real and inverted
• C. Real and diminished
• D. None of the above

Answer 1

The correct option is A Virtual and erect

Before shifting the candle,

$u=12-50=-38cm$

$v=88-50=38cm$

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

$\frac{1}{f}=\frac{1}{38}+\frac{1}{38}$

$\frac{1}{f}=\frac{1+1}{38}$

$f=19cm$

Hence, before shifting the candle, it is placed at a distance of $2f$ from the mirror.

When candle is shifted towards the lens from this position, its distance from the lens is $f<u<2f$. In this scenario, image formed is virtual, diminished and erect.