Question
Use the mirror equation to show that an object placed between f and 2f of a concave mirror produces a real image beyond 2f?
Solution
Mirror formula is given by,
where,
u is the distance of the object from the mirror,
v is the distance of image from the mirror, and
f is the focal-length of the mirror.
For a concave mirror, f < 0.
Object distance is negative for an object on the left side. i.e., u< 0.
Given, f < u <2f.
Subtracting throughout from 
, we get
Therefore, the image formed is negative and is on the left side.
Also, the inequality implies, 2f > v. i.e., |2f| < |v|.
That is, the real image is formed beyond 2f.
