Doppler Effect

A tuning fork of frequency 400Hz is moved away from an observer toward a flat wall with a speed of 2 m/s. What is the apparent frequency (a) of the unreflected sound waves coming towards the observer, and (b) of the sound waves coming to the observer after reflection? (c) How many beats per second are heard? Assume the speed of sound in the air is 340m/s?

Refraction

• 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 PHYSICS, 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.)

http://www.youtube.com/watch?v=OdcHCRF00jM

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

• The fish is deeper than it appears.

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

• 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).

• Q3:What did you observe?As the water level rises, the coin becomes visible.

• 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.

• The coin appears to be slightly magnified.

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?

The light is bent at the interface between the air and water.

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

• Light must be bent away from the normal as it leaves the water in order for your eye to see the coin.

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

• Dependent on answer to question 1 & 2.• 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)You can not reach the drain plug. Light reflected off the drain is bent away from the normal as the ray leaves the water. Therefore the drain's position appears to be shallower than it actually is. It also appears magnified adding to the perception of being closer.

• Find the intensity levels in decibels for sounds with intensities of (a) I= 10-2 W/m2,

(b)I=10-6 W/m2, and (c) I=10-15 W/m2.