Test3Shih - Platt, David Quiz 2 Due: Oct 18 2005, 10:00 pm...

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Unformatted text preview: Platt, David Quiz 2 Due: Oct 18 2005, 10:00 pm Inst: Ken Shih 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points A variable resistor is connected across a con- stant voltage source. Which of the following graphs represents the power P dissipated by the resistor as a function of its resistance R ? 1. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 2. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 3. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 4. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 5. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 6. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 7. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) cor- rect Explanation: The power dissipated in the resistor has several expressions P = E I = E 2 R = I 2 R , where the last two are simply derived from the first equation together with the application of the Ohms law. Since the resistor is connected to a constant voltage source E = constant P = E 2 R = constant R , tells us that the power is inversely propor- tional to the resistance P 1 R . 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 002 (part 1 of 3) 10 points A rectangular loop consists of 333 closely wrapped turns of wire and has dimensions . 17 m by 0 . 25 m. The loop is hinged along the y-axis, and its plane makes an angle of = 12 with the x-axis. A uniform magnetic field of 0 . 85 T is di- rected along the x-axis and the current in the loop is 3 . 2 A in the direction shown. Platt, David Quiz 2 Due: Oct 18 2005, 10:00 pm Inst: Ken Shih 2 x y z 1 2 B = 0 . 85 T B = 0 . 85 T . 17m . 2 5 m i = 3 . 2 A What is the magnitude of the torque ex- erted on the loop? Correct answer: 37 . 6536 Nm. Explanation: Let : n = 333 , = 0 . 17 m , w = 0 . 25 m , = 12 , B = 0 . 85 T , and I = 3 . 2 A . The field makes an angle of = 90 - with a line perpendicular to the plane of the loop, so the torque acting on the loop is = n B I A sin = n B I w sin (1) = (333)(0 . 85 T)(3 . 2 A)(0 . 17 m)(0 . 25 m) sin(90 - 12 ) = 37 . 6536 Nm . 003 (part 2 of 3) 10 points Assume that is measured in the positive direction; i.e. , clockwise (looking down from above) as shown in the figure. If the loop is at rest, the magnetic torque will 1. try to lift the loop along the y-axis. 2. try to make larger. correct 3. try to make smaller. 4. not affect . 5. None of these 6. try to lower the loop along the y-axis. Explanation: The right hand rule shows that torque tends to rotate the loop clockwise as viewed from above....
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Test3Shih - Platt, David Quiz 2 Due: Oct 18 2005, 10:00 pm...

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