Aim below if using the spear. Aim directly if using a laser.
Work Step by Step
When light exits water into air, it bends away from the normal. As explained on page 528 and shown in Figure 28.28, this effect causes submerged objects to appear closer to the surface than they actually are. The fish is physically located below where you see it, so you should aim your spear below its observed position. However, in tagging the fish with a laser, simply aim straight at the fish. The light from the fish refracts as it travels to you. Your laser will follow the same path back to the fish, bending toward the normal as it enters the water.