Question

The magnitude of focal length of a concave mirror is $f$. An object is placed at a distance $x$ from the focus and forms a real image. The magnification is:

• A. $-\frac{f}{x}$
• B. $-\frac{x}{f}$
• C. $-\frac{f}{f-x}$
• D. $\frac{x}{x-f}$

Answer 1

The correct option is A $-\frac{f}{x}$

The magnification of a concave mirror is given by:
$m=-\frac{f}{f-u}$
Now, for the given case, $u$ is the object distance which is equal to: $u=f+x$
Substituting this value in the expression for magnification, we get:
$m=-\frac{f}{f-(f+x)}$
This, gives us the value of $m$ to be $\frac{-f}{x}$