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

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​

Answer 1

Answer:

As we have learned

Mirror Formula -

frac{1}{v}+frac{1}{u}=frac{1}{f}

 

- wherein

u= Object distance from pole of mirror.

v= Image distance from pole of mirror.

f= focal length of the mirror.

 

u_{1}= -40cm

f= -15cm

\frac{1}{v_{1}}=\frac{1}{f_{1}}-\frac{1}{u_{1}}=\frac{-1}{15}+\frac{1}{40}=\frac{-8+3}{120}=\frac{-5}{120}

{v_{1}= -24cm

2nd case  

{v_{2}}= -20cm

\frac{1}{v_{2}}=\frac{1}{f}-\frac{1}{u_{2}}=\frac{-1}{15}+\frac{1}{20}=\frac{-4+3}{60}

v_{2}=-60cm

Image gets displaced by 36 cm , away from the mirror  

 

 

 

 

Option 1)

30 cm towards the mirror

This is incorrect

Option 2)

36 cm away from the mirror

This is correct

Option 3)nation:

Answer 2

Answer:

B. 36cm away from the mirror.

Explanation:

1. From the given question the image will be formed between F and CF .
2. when the object is in 20cm the image will be formed beyond CF