The focal length of a concave mirror is 20 cm. What is its radius of curvature?
A) 10 cm
B) 40 cm
C) -40 cm
D) 20 cm
E) -20 cm

Question

Quizplus · Accepted Answer

The relationship between the focal length (f) and the radius of curvature (R) for a concave mirror is given by the equation: 
1/f = 1/R - 1/d
where d is the object distance from the mirror. When the object is at infinity (i.e. parallel rays), the object distance is effectively infinite, so we can ignore the 1/d term. Therefore, we can rearrange the equation to solve for R:
1/R = 1/f
R = f*1 = 20 cm * 1 = 40 cm
Therefore, the radius of curvature is 40 cm. Choice B is the correct answer.

The Focal Length of a Concave Mirror Is 20 Cm