Geometric Optics


Seat Experiment

Spearfishing: You are spearfishing from the bank of a pond. You are looking into the water from above at an angle, and you see a fish beneath the surface. Having taken PHY 112, you are aware that light bends (refracts) when it passes through the water/air interface. Therefore, light reflecting off the fish bends before striking your eye and the fish is not where it appears to be. 

Q1: Is the fish deeper or shallower than its image appears to be? (Using a sketch explain your reasoning.) 

Q2: Should you stab above or below the image of the fish to spear it? (Explain your reasoning using a sketch.)

Place a coin in the bottom of a cup.

Move your head to an angle where the coin is just out-of-sight behind the rim of the cup.

Add water to the cup with out moving your head. Describe what you see.

Q3: What did you observe? 

Q4: How did the image of the coin viewed through the water compare to simply looking at the coin? Compare the apparent size of the coin. 

Q5: Draw two ray diagrams for your eye, the coin, and the cup, one with and one without water. Does the light bend in either case? 

Q6: Use your diagrams to explain what you observed, describe how light must change paths. 

Q7: Now re-address (discuss and amend your responses for) the spearfishing questions.

Q8: You are hired by the neighborhood greasy spoon restaurant, and assigned to wash dishes in an industrial sized sink. You see the drain plug on the bottom through the cold, greasy water and it looks like it is just barely within reach. Can you pull it out by hand? Why or why not? (Physical science reasons, please). 


Seat Activities