The driving mirror of a car has a radius of curvature of 1m. A vehicle behind the car is 4m from the mirror. Find the image distance behind the mirror.
A. 8/7 B. 4/9 C. 9/2 D. 4/7
Correct Answer: B
Explanation
A driving mirror is always a convex mirror which is always of negative focal length and always forms a virtual image Thus if r = 1m = 100cm f = 1/2 = -50 ∴ if U = 4cm = 400cm f = -50cm ∴1/u + 1/v = 1/f 1/400 + 1/v = -1/50 ∴ -1/v = 1/400 + 1/50 -1/v = (1 + 8)/400 = 9/400 ∴ v = -400/9 v = 4/9
