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# Problems4_2010 - of the ribbon and a transverse voltage...

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Physics 205. Fall 2010. Problem set 4. 1. Two insulated wires in the x-y plane cross at a 30 o angle but do not make electrical contact. Each wire carries 5.0 A current (the angle between current directions is 30 0 ). Find magnetic field in two non-equivalent points located 4.0 cm from the intersection, in the x-y plane, at equal distances from both wires. Hint: making a drawing will be very helpful. 24 points 2. Radio-astronomers detect electromagnetic radiation with frequency of 45 MHz (1 Hz = 1s -1 ) from an interstellar gas cloud. They suspect this radiation is emitted by electrons spiraling in a magnetic field. That is the magnetic field magnitude inside the gas cloud? Hint: you do not know about the radiation emitted by accelerating electrons yet, but use the intuitively appealing (correct) guess: the frequency of radiation is the same as the frequency of circular motion. 24 points. 3. A flat metal ribbon of width 2.0 mm and thickness of 150 μ m is immersed in a perpendicular magnetic field of strength 1 T. A current of 1.5A is passed along the length
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Unformatted text preview: of the ribbon and a transverse voltage equal to 50 μ V is measured across the width. What is the average velocity of electrons in metal? What is the number of conducting electrons per unit volume of this metal? 24 points. 4. Two wires, each having a weight per unit length of 10 –4 N/m, are strung parallel, one 0.2 m above the other. If the wires carry the current of same magnitude, how great must the current in each wire be for the magnetic field due to the lower conductor to balance the weight of the upper conductor? What have to be the directions of the two currents for that to work? 24 points. 5. A flat uniformly charged disk with radius 10 cm and total charge of 10 μ C spins at a rate of 100 turns per second around its axis. What is the magnetic field magnitude next to the center of the disk? Hint: this problem most likely requires integration. 24 points....
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