A spherical lightbulb of diameter 3.20 cm radiates light equally in all directions, with power 4.50 W.
(a) Find the light intensity at the surface of the bulb.
(b) Find the light intensity 7.20 m away from the center of the bulb.
(c) At this 7.20-m distance a lens is set up with its axis pointing toward the bulb. The lens has a circular face with a diameter 15.0 cm and has a focal length of 35.0 cm. Find the diameter of the image of the bulb.
(d) Find the light intensity at the image.