If we want to obtain a virtual and magnified image of an object by using a concave mirror of focal length 18…
If we want to obtain a virtual and magnified image of an object by using a concave mirror of focal length 18 cm, where should the object be placed? Use mirror formula to determine the object distance for an image of magnification +2 produced by this mirror to justify your answer.
Solution
Object should be placed between F and P / At less than 18cm distance from the mirror.
Mirror formula = $\dfrac{1}{v}$ + $\dfrac{1}{u}$ = $\dfrac{1}{f}$
Magnification m = +2
f = -18 cm
m = -v/u = +2
therefore v = -2u
1/2u + $\dfrac{1}{u}$ = 1/-18cm
therefore 1/2u = 1/-18cm
u = -9 cm