true or false? the focal length of a converging lens in h20 is larger in abs value compared to its f in air?

Question

please help. i know its true but why?

Answer 1

It's true because by Snell's law (ηsinθ1 = η2sinθ2) there is a smaller refraction angle (difference between θ1 and θ2) when the values of index of refraction η are more nearly equal. η of air ~= 1 while η of water ~= 1.33, closer to that of glass ~= 1.5 to 2. Think of what the f would be if the lens were 'immersed' in glass: infinite, right?