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Unformatted text preview: ap, while the solid copper sheet was stopped between the poles of the magnet. This demonstrates which law? Explain. Lenz’s or Faraday’s Law: The opposing induced current is much bigger in the solid sheet. He slots in the other sheet break up thecurrents, making the opposing field it produces much smaller. 2. A 341 Hz tuning fork excites what wavelength of sound in a column of class room air 25 cm long? Λ=c/f=341/341=1m. I gave the 25 cm which is what you would measure in the lab experiment we did=1/4 λ. You did not need it here. 3. Two tuning forks as in problem #2 are made to oscillate in phase. One is 1.5 m directly in front of you and the other 2.0 m in front of you. What do you hear? Explain, perhaps drawing a picture. The tuning forks send sound from positions ½ λ apart, so they DESTRUCTIVELY interfere, cancelling each other, so that you hear no sound. 4. How far apart are the hot spots when cooking in a microwave oven (no turn table)? Show your calculation. λ/2=c/f=3x108/2450x106=12 cm (λ/2 because that is the distance between maxima in the standing wave). 5. You rub a plastic straw, charging it, and wave it up and down 3 times per second. What is the frequency of E‐M radia...
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- Fall '09