Question
(a) Calculate the distance of an object of height h from a concave mirror of radius of curvature 20 cm, so as to obtain a real image of magnification 2. Find the location of image also.
(b) Using mirror formula, explain why does a convex mirror always produce a virtual image.
Solution
a)
Given,
Radius of curvature, R = 20 cm
So, focal length, f = R/2 = - 10 cm
Since the image obtained is real, therefore magnification of the image, m = -2
Now, using the formula, 
Therefore, the distance of the object is 15 cm in front of the mirror and the position of the image is 30 cm, formed in front of the mirror.
b)
For a convex mirror,
Focal length, f > 0
Position of the object, u < 0
Using mirror formula, we have
That is, the image formed by a convex lens is always behind the mirror and hence is virtual.
