### NEET Solved Paper 2018 Question 20

##### Question: An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be [NEET - 2018]

#### Options:

A) 30 cm towards the mirror

B) 36 cm away from the mirror

C) 30 cm away from the mirror

D) 36 cm towards the mirror

## Show Answer

#### Answer:

Correct Answer: B

#### Solution:

$ \frac{1}{f}=\frac{1}{v _1}+\frac{1}{u} $ $ -\frac{1}{15}=\frac{1}{v _1}-\frac{1}{40} $

$ \Rightarrow \frac{1}{v _1}=\frac{1}{-15}+\frac{1}{40} $ $ v _1=-24cm $ .

When object is displaced by 20 cm towards mirror.

Now, $ u _2=-20 $ $ \frac{1}{f}=\frac{1}{v _2}+\frac{1}{u _2} $ $ \frac{1}{-15}=\frac{1}{v _2}-\frac{1}{20} $ $ \frac{1}{v _2}=\frac{1}{20}-\frac{1}{15} $ $ v _2=-60cm $

So, image shifts away from mirror by $ =60-24=36cm $ .