Chapter 29, Problem 40A

If you were spearing a fish with a spear, would you aim above, below, or directly at the observed fish to make a direct hit? Would your answer be the same if you used laser light to ’spear' the fish? Defend your answer.

To determine

To Explain: The direction along which the spear and the laser should be aimed for it hit the fish directly.

Explanation of Solution

Introduction: 

The light coming from a fish refracts away from the normal because it moves through the water surface to the eyes. Due to this, the fish seems closer to the surface than its real position.

Explanation: 

When the arrow would enter the water, it will not deviate. It will continue along its straight-line path from the bow. So, to strike the fish, the spear should be aimed below where the fish seems to be. In another case, laser is used to hit the fish. Laser beam would be refracted on entering the water. The laser beam will cover the same pathway as the light from the fish reaches the eye, but in opposite direction. So, to strike the fish, one should aim the laser gun directly where the fish seems to be.

Conclusion: 

The fish appears at the shallower depth, so the observer should point the spear/laser at the image below the observed fish.