Question

A student is using a convex lens of focal length 10 cm to study the image formation by a convex lens for the various positions of the object. In one of his observations, he may observe that when the object is placed at a distance of 20 cm from the lens, its image is formed at (select the correct option)

• A. 20 cm on the other side of the lens and is of the same size, real and erect.
• B. 40 cm on the other side of the lens and is magnified, real and inverted.
• C. 20 cm on the other side of the lens and is of the same size, real and inverted.
• D. 20 cm on the other side of the lens and is of the same size, virtual and erect.

Answer 1

Answer: (C)

20 cm on the other side of the lens and is of the same size, real and inverted.

Focal length of the lens, $f=10cm$
Object distance,$u=-20cm$ (negative sign is used due to sign convention)
Using the lens formula:

$\frac{1}{u}+\frac{1}{f}=\frac{1}{v}$
Substituting the values in the above equation we get,
$\Rightarrow v=20cm$
Hence, the image will be formed on the other side of the lens.
Magnification is given as:
$m=\frac{imagedistance}{objectdistance}=\frac{20}{20}=1$
Therefore, the image formed by the convex lens will be of same size, real and inverted.
Hence, the correct option is C.