1) At a concert you sit 12 m directly in front of one of the two speakers on the front of the stage. The other speaker is 8 m from the first. What frequencies in the human hearing range will sound soft to you? (Just get the first two or three!)

[70, 210, 350,...]

2)Two tweeters (high frequency speakers) are separated by 20 cm. You are sitting at an angle of 15 degrees from the center line of the speakers. When a pure tone (sine wave) is played through the speakers you hear nothing. What is a possible frequency of the tone?

[3.3 kHz]

3) Laser light of wavelength 630 nm shines on two narrow slits separated by 1.0 mm. a screen is placed 2 m in front of the slits. Where are the bright spots on the screen? (How far apart are they?)

[1.2 mm]

4) You are standing next to a long concrete wall with a speaker. If you place the speaker 10 m away from you and the same distance from the wall you observe that you cannot hear the 68 Hz sound being played. How far are you and the speaker from the wall? HINT: consider the two paths the sound must take to reach you - one is direct and one is reflected.

[3.7 m]

5) Two speakers separated by 80 cm are producing sound at 750 Hz. 4.0 m away a microphone is placed along the centerline between the speakers. Will the microphone detect a loud sound (relatively speaking) or a soft one at this point? Will the sound get louder or softer as the microphone is moved perpendicularly away from the centerline? Explain your reasoning.

6) Continuing to explore the situation in #5 - how far from the centerline will you need to move the microphone until it detects no sound at all (assuming no irritating reflections from walls or observers:)? How much further will you need to move it to find another "loud" spot?

7) Suppose you have a single speaker and a couple of long pieces of 4" flexible plastic pipe. I have seen this pipe used to carry human voices for remarkable distances in the corn mazes that people explore around halloween each year. Suppose further that one piece of pipe is 1.2 m longer that the other and the far ends of the pipes are placed in front of the cranked up speaker. The near ends of the tubes are placed together right in front of you. Determine at least one frequency that will be heard loudly and one that will be very hard to hear in this situation. -- I admit I haven't tried this but it seems pretty intriguing.

8) You are exploring a far away beach when you notice that there is a regular erosional pattern on the beach. You estimate that the regions of high erosion are separated by a distance of 40 m. The waves have a wavelength of 15 m and a speed of 2.5 m/s. As you look out into the sea you observe evidence of a reef 500m offshore. Based on this evidence you expect to see openings in the reef separated by what distance?

[187 m]

9) So here's a cool one ...... Suppose you have two speakers 4 m apart putting out a constant sound at 1500 Hz. You are standing on the midline of the speakers 100 m away. One of the speakers is mounted on rollers and is moving parallel to the midline at 6 m/s. What is the beat frequency you observe? Think about why there is a beat frequency. Happy Hunting!