An object is placed at a distance of 20 cm in front of a concave mirror. The mirror forms a real image that is three times the size of the object. The radius of curvature of the mirror is :

Step-by-step solution

Given object distance u = -20 cm . Since the image formed by the concave mirror is real and magnified three times, the lateral magnification is m = -3 . The relation between magnification, focal length, and object distance is given by: m = f f - u Substituting the given values: -3 = f f - (-20) -3(f + 20) = f -3f - 60 = f -4f = 60 f = -15 cm The radius of curvature is R = 2f : R = 2(-15 cm ) = -30 cm Answer: -30 cm