17homework13 - Husain, Zeena Homework 13 Due: Apr 27 2004,...

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Unformatted text preview: Husain, Zeena Homework 13 Due: Apr 27 2004, 4:00 am Inst: Sonia Paban 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page find all choices before making your selection. The due time is Central time. 001 (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 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 y-axis, ~ E is along the negative z-axis. 4. ~ B is along the negative z-axis, ~ E is along the negative y-axis. 5. ~ B is along the positive y-axis, ~ E is along the positive z-axis. 6. ~ B is along the positive z-axis, ~ E is along the positive y-axis. 7. ~ B is along the negative z-axis, ~ E is along the positive y-axis. correct 8. ~ B is along the negative z-axis, ~ E is along the positive z-axis. 9. ~ B is along the negative y-axis, ~ E is along the positive y-axis. 10. ~ B is along the positive y-axis, ~ E is along the negative z-axis. 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. 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 , there is a companion E- field stretched out from D to A . Notice that the electromagnetic wave is traveling along the negative x-axis, so ~ E has to be directed along the positive y-axis (so that ~ E ~ B is directed along the correct direction). Husain, Zeena Homework 13 Due: Apr 27 2004, 4:00 am Inst: Sonia Paban 2 002 (part 2 of 2) 10 points Now consider the current sheet which under- goes the sinusoidal oscillations with a definite frequency where the amplitude of the mag- netic field oscillations in the waves is B max . Consider a book of area A located at P paral- lel to the yz plane. Find the radiation force on the book, if it absorbs one third of the light....
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This note was uploaded on 10/13/2009 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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17homework13 - Husain, Zeena Homework 13 Due: Apr 27 2004,...

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