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Unformatted text preview: midterm 03 VARELA, CHRISTOPHER Due: Nov 15 2007, 11:00 pm 1 Question 1, chap 32, sect 5. part 1 of 1 10 points In a series RLC ac circuit, the resistance is 8 , the inductance is 25 mH, and the capac- itance is 24 F. The maximum potential is 219 V, and the angular frequency is 100 rad / s. Calculate the maximum current in the cir- cuit. Correct answer: 0 . 528674 (choice number 8). Explanation: Let : R = 8 , L = 25 mH = 0 . 025 H , C = 24 F = 2 . 4 10 5 F , V max = 219 V , and = 100 rad / s . The capacitive reactance is X C = 1 C = 1 (100 rad / s) (2 . 4 10 5 F) = 416 . 667 . The inductive reactance is X L = L = (100 rad / s) (0 . 025 H) = 2 . 5 . The maximum current is I max = V max Z = V max radicalbig R 2 + ( X L X C ) 2 = 219 V radicalbig (8 ) 2 + (2 . 5 416 . 667 ) 2 = . 528674 A . Question 2, chap 31, sect 2. part 1 of 1 10 points A coil is wrapped with 375 turns of wire on the perimeter of a circular frame (of radius 82 cm). Each turn has the same area, equal to that of the frame. A uniform magnetic field is directed perpendicular to the plane of the coil. This field changes at a constant rate from 26 mT to 69 mT in 50 ms. What is the magnitude of the induced E in the coil at the instant the magnetic field has a magnitude of 36 mT? Correct answer: 681 . 251 (choice number 10). Explanation: Basic Concepts: E = N d B dt B integraldisplay vector B d vector A = B A Solution: E = N d B dt = N A B t = N r 2 ( B 2 B 1 ) t = (375) (82 cm) 2 (69 mT) (26 mT) 50 ms = 681 . 251 V |E| = 681 . 251 V . Question 3, chap 33, sect 5. part 1 of 1 10 points Consider an electromagnetic wave pattern as shown in the figure below. E B midterm 03 VARELA, CHRISTOPHER Due: Nov 15 2007, 11:00 pm 2 The wave is 1. traveling right to left. 2. traveling left to right. correct 3. a standing wave and is stationary. Explanation: The vector E vector and vector B vector are not at the same point on the velocity axis. Pick an instant in time, where the E and B fields are at the same point on the velocity axis. z v x y E B For instance, let us choose the point where the vector E vector is along the x axis, as shown in the above figures. At this same instant, the vector B vector is along the negative y axis (at a point with a phase difference of 360 from the place on the velocity ( z ) axis where the vector E vector is drawn). Then vector E vector B is along the negative z axis. Therefore, the electromagnetic wave is traveling left to right. Question 4, chap 31, sect 3. part 1 of 2 10 points A horizontal circular wire loop of radius . 7 m lies in a plane perpendicular to a uni- form magnetic field pointing from above into the plane of the loop, has a magnitude of . 52 T....
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This note was uploaded on 09/07/2010 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
- Spring '08