Thin Converging Lens Challenge

A thin converging lens produces a real image. The graph shows how the image distance varies with the object distance for the lens. 

(a) Determine the focal length of the lens.

A person takes a picture of a waterweed in a fishbowl using a camera with the thin converging lens.The fishbowl is filled with water. When the film, lens, and waterweed are positioned as shown in the figure below, a clear image of the waterweed is recorded on the film. 

(b) Determine the refractive index of water.

Ans: (a) 5 cm; 1.33

Acknowledgement: Part (b) is modified from IJSO 2015 MCQ Question 16.