Question

From a concave mirror of focal length $20cm$. Match the following:

Answer 1

Given,

$f=-20cm$ of concave lens.

We know,

In case of mirror,

If object and image distance have opposite signs,

Then they are of opposite nature (if object real then image virtual),

Also,

The image is erect with respect to object.

And,

Mirror formula$\to \frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

Magnification=$\frac{-v}{u}$

$\text{Part A}$

$u=-10$

From mirror formula,

$v=20cm$

$m=2$ (magnified).

As v and u have opposite signs,

So image is erect,virtual,and magnified. $\text{A}\to 4$

$\text{Part B}$

$u=-30$

From mirror formula,

$v=-60cm$

$m=-2$

As v and u have same sign,

So image is inverted,real and magnified. $\text{B}\to 2$

$\text{Part C}$

$u=-40$

From mirror formula,

$v=-40cm$

$m=-1$

As v and u have same sign,

So image is inverted,real and same size. $\text{C}\to 1$

$\text{Part D}$

$u=-50$

From mirror formula,

$v=-100/3cm$

$m=-2/3$

As v and u have same sign,

So image is inverted,real and small. $\text{D}\to 3$