9. Ray optics abd optical instruments — Physics STD 12 Science — Question

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

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

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.