From kirchoffs laws the loop equations for the right

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From Kirchoff’s laws, the loop equations for the right and left loops respectively are right loop : 1 5 E + i 1 R = 0 (1) left loop : 4 5 E + i 2 R = 0 (2) 004 (part 1 of 1) 10 points In the figure shown, the north pole of the magnet is first moved down toward the loop of wire, then is withdrawn upward. Clockwise Counter- clockwise N As viewed from above, the induced current in the loop is 1. first clockwise, then counterclockwise. 2. for both cases counterclockwise with de- creasing magnitude. 3. first counterclockwise, then clockwise. correct
Husain, Zeena – Exam 3 – Due: Apr 13 2004, 10:00 pm – Inst: Sonia Paban 3 4. for both cases counterclockwise with in- creasing magnitude. 5. for both cases clockwise with decreasing magnitude. 6. for both cases clockwise with increasing magnitude. Explanation: From Ohm’s law and Faraday’s law, the current in magnitude is I = V R = - 1 R d Φ dt , where Φ is the magnetic flux through the loop. We know the sign of the rate of change of the magnetic flux is changed when the magnet is withdrawn upward, which, according to the equation the direction of the current is also changed. From Lenz’s law, we know when the magnet is moved down toward the loop, the current in the loop is counterclockwise as viewed from above. 005 (part 1 of 2) 10 points To demonstrate the generation of electromag- netic waves due to oscillations of a current sheet in the yz -plane at x = 0, one first con- siders the following situation. One turns on a steady current flow along the negative y -axis at t = 0. p z I x y 0 The point P is along the negative x - direction. Let ~ B and ~ E be the magnetic and electric field established at P soon after the switching on of the current, respectively. The directions of ~ B and ~ E are 1. ~ B is along the positive z -axis, ~ E is along the negative y -axis. 2. ~ B is along the negative y -axis, ~ E is along the positive z -axis. 3. ~ B is along the negative z -axis, ~ E is along the negative y -axis. 4. ~ B is along the negative y -axis, ~ E is along the positive y -axis. 5. ~ B is along the positive z -axis, ~ E is along the positive y -axis. 6. ~ B is along the positive y -axis, ~ E is along the negative z -axis. 7. ~ B is along the positive y -axis, ~ E is along the positive z -axis. 8. ~ B is along the negative y -axis, ~ E is along the negative z -axis. 9. ~ B is along the negative z -axis, ~ E is along the positive z -axis. 10. ~ B is along the negative z -axis, ~ E is along the positive y -axis. correct Explanation: Basic Concepts Electromagnetic waves. Since the current on the sheet is flowing along the negative y -axis, the magnetic field for neg- ative values of x is directed along the negative z -axis.
Husain, Zeena – Exam 3 – Due: Apr 13 2004, 10:00 pm – Inst: Sonia Paban 4 x y O O z P P E E B B B A C D About point P we may construct a rectan- gular window ABCDA in the xy -plane. As the “front” of the B -field sweeps across the window to the left, it causes a counterclock- wise induced emf, which is generated by the induced emf at the right side of the window from D to A . Since the side DA can be placed at any location between O and P , when the B -field reaches P

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