Question

A pin of length $2cm$ along the principle axis of a converging lens, the centre being at a distance of $11cm$ from the lens. The focal length of the lens is $6cm$. Find the size of the image ?

• A. $3cm$
• B. $2.4cm$
• C. $10cm$
• D. $5cm$

Answer 1

The correct option is A $3cm$

REF.Image.

Now we have to calculate the image of A and B. Let the images be A', B'. So, length

of A' B' = size of image.

For A, u = -10 cm, f = 6 cm

Since, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\Rightarrow \frac{1}{v}-\frac{1}{-10}=\frac{1}{6}$

$\Rightarrow v=15cm=O{A}^{\prime }$

For B, u = -12 cm, f = 6 cm

Again, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\Rightarrow \frac{1}{v}=\frac{1}{6}-\frac{1}{12}$

$\Rightarrow$ v = 12 cm = OB'

$\therefore$ A'B' = OA' - OB' = 15 - 12 = 3 cm.

So, size of image = 3 cm.