In the Figure,the Radius of Curvature of the Curved Part

Multiple Choice

In the figure,the radius of curvature of the curved part of the lens is 35.0 cm,and the refractive index of the lens material is 1.620.What is the focal length of the lens?

A) +56.5 cm
B) -56.5 cm
C) +28.2 cm
D) +21.6 cm
E) -21.6 cm