Fall 2012 Midterm 3 Solutions

Path 2 is larger than path 1 because it surrounds

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Unformatted text preview: h 1 because it surrounds more flux than path 1, but smaller than 3 and 4 because it does not surround all of the flux. 1, then 2 and 4 tie, then 3 all tie 4, 1, 3, 2 1, 4, then 2 and 3 tie 1,2, then 3 and 4 tie Version 1 Page 6 11. A solid conductor of radius a is supported by insulating disks on the axis of a conducting tube with inner radius b and outer radius c as shown in the figure. The central conductor and the tube carry equal currents in opposite directions. The currents are distributed uniformly over the cross sections of each conductor. Which one of the following statements about the magnetic field created by this arrangement is FALSE. A) B) C) D) E) B is a maximum at r=a. B=0 for r>c B decreases to zero as you go from r=b to r=c. B is proportional to 1/r for r<a B is proportional to 1/r for a<r<b Version 1 Page 7 12. The AC generator in a hydroelectric power plant supplies a small town with an RMS current of 4000 A at 120 V rms. At the power plant a 50-to-1 step up transformer is used prior to high voltage transmission. Near the town a substation has a 100-to-1 step down transformer and then each house has a nearby 20-to-1 step down transformer to provide a safe, low voltage. Assuming ideal transformers and no transmission losses what RMS current must be produced in the AC generator? 50-1 Step up A) B) C) D) E) 100-1 HV transmission 20-1 Step down Step down 141 A 40,000 A 100 A 25 A 1000 A 4000 A rms Remember, N_s < N_p in a step down transformer. We have to work backwards t...
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