A glass slab surrounded by air causes a sideways displacement in a beam of light.
(a) If the slab is now placed in water, does the displacement it causes increase, decrease, or stay the same?
(b) Choose the best explanation from among the following:
I. The displacement of the beam increases because of the increased refraction due to the water.
II. The displacement of the beam is decreased because with water surrounding the slab there is a smaller difference in index of refraction between the slab and its surroundings.
III. The displacement stays the same because it is determined only by the properties of the slab; in particular, the material it is made of and its thickness.