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: Option 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