Question

An object is placed 25 cm in front of a concave mirror of focal length 12.5 cm. At what distance from the mirror should the screen be placed so that a sharp image is obtained.

Answer 1

AnsWer :

-25 cm.

Given :

• Object distance (u) = -25 Cm.
• Focal length (f) = -12.5 Cm.
• Image distance (v) = ?

Solution :

As we know, the formula of mirror.

$\boxed { \tt \frac{1}{ \red{f}} = \frac{1}{ \red{v}} + \frac{1}{ \red{u}} .}$

Where as,

• (f) focal length.
• (v) Image distance.
• (u) Object distance.

Now,

Putting value, which given above.

$\implies \tt\frac{1}{ - 12.5} = \frac{1}{v} + \frac{1}{ - 25}$

$\implies \tt \frac{1}{25} - \frac{10}{ 12 \cancel.5} = \frac{1}{v}$

$\implies \tt \frac{1}{v} = \frac{5 - 10}{125}$

$\implies \tt \frac{1}{v} = \frac{ - \cancel5}{ \cancel{125}}$

$\implies \tt \frac{1}{v} = \frac{ - 1}{25}$

$\implies \tt v= - 25 \: cm.$

Therefore, When we place the Image (v) at 25 Cm so that a sharp image obtained on screen.