Question

The image formed by a concave mirror is:

• A. always real.
• B. always virtual.
• C. certainly real if the object is virtual.
• D. certianly virtual if the object is real.

Answer 1

Answer: (C)

certainly real if the object is virtual.

Using mirror equation,

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

$\frac{1}{v}=\frac{1}{f}-\frac{1}{u}$

For concave mirror, focal length is negative. Hence, $f<0$

For a virtual object, object distance is positive. Hence $u_v>0$

From above, it can be observed that image distance $v$ is negative when object is virtual. Since image distance is negative, it is formed by real intersection of rays and image is real.

For a real object, object distance is negative. Hence $u_r<0$

In this case, image distance $v$ may be positive or negative depending on the location of object.

Hence, only option C is correct.