Question

Ms. Johnson points a laser pointer from a certain angle toward the bottom of an empty aquarium. Her students see the reflection of its rays at the bottom of the aquarium.

A hand holding a laser pointer toward the bottom of an aquarium and the end of the beam is reflected at the bottom of the aquarium.

She then partially fills the aquarium and points the laser pointer from the same height and angle as before.

A laser pointer pointing toward water in an aquarium.

Predict whether or not the reflected spot of light will be in the same place as it was when she pointed the laser pointer into the empty aquarium. Explain your reasoning.

Answer 1

The reflected spot will appear to be closer than when the aquarium was empty.

N1 sin θ1 = N2 sin θ2 N1 is in air and equals 1, N2 is greater than one

θ2 is measured from the vertical and the ray is less than θ1

The distance to spot is less so it appears closer

(Consider a spot directly below the pointer L1 = N2 L2)

If N2 = 4/3 then L2 would be 3/4 L1