A plano-concave lens having index of refraction 1.50 is placed on a flat glass plate as shown in the figure below. Its curved surface, with radius of curvature 8.35 m, is on the bottom. The lens is illuminated from above with yellow sodium light of wavelength 592 nm, and a series of concentric bright and dark rings is observed by reflection. The interference pattern has a dark spot at the center that is surrounded by 42 dark rings, the largest of which is at the outer edge of the lens. (a) What is the thickness of the air layer at the center of the interference pattern? um (b) Calculate the radius of the outermost dark ring. 49.178 cm (c) Find the focal length of the lens. 24.59 m

A plano-concave lens having index of refraction 1.50 is placed on a flat glass plate as shown in the figure below. Its curved surface, with radius of curvature 8.35 m, is on the bottom. The lens is illuminated from above with yellow sodium light of wavelength 592 nm, and a series of concentric bright and dark rings is observed by reflection. The interference pattern has a dark spot at the center that is surrounded by 42 dark rings, the largest of which is at the outer edge of the lens. (a) What is the thickness of the air layer at the center of the interference pattern? um (b) Calculate the radius of the outermost dark ring. 49.178 cm (c) Find the focal length of the lens. 24.59 m