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Unformatted text preview: ragsdale (zdr82) – HW10 – ditmire – (58335) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 3) 10.0 points A plane electromagnetic wave is generated due to the initiation of current along the y direction in a current sheet in the xy plane at z = 0. A steady flow current is switched on at t = 0. This current sheet generates a traveling “front” of the electric and magnetic fields. z x y infinite current sheet in x, y plane Current is in + y direction, as shown by arrows. P z Consider the case at the instant when the “front” is at the point P z on the positive z axis. Determine the direction of vector B at P z . 1. hatwide B P is in the + x direction correct 2. hatwide B P is in the + y direction 3. hatwide B P is in the − y direction 4. hatwide B P is in the − z direction 5. hatwide B P is in the + z direction 6. hatwide B P is in the − x direction Explanation: Basic Concepts: EM Wave and Poynting Vector. Solution: By inspection, the right-hand-rule implies that the direction of vector B at P z is along + x . 002 (part 2 of 3) 10.0 points Determine the direction of the Poynting vec- tor vector S at P z . 1. hatwide S P is in the + x direction 2. hatwide S P is in the − y direction 3. hatwide S P is in the + y direction 4. hatwide S P is in the − x direction 5. hatwide S P is in the + z direction correct 6. hatwide S P is in the − z direction Explanation: The traveling field pattern is moving away from the source in the + z direction. 003 (part 3 of 3) 10.0 points Determine the direction of vector E at P z . 1. hatwide E P is in the − x direction 2. hatwide E P is in the − z direction 3. hatwide E P is in the + x direction 4. hatwide E P is in the + z direction 5. hatwide E P is in the + y direction 6. hatwide E P is in the − y direction correct Explanation: The induced electric field vector E must flow in the direction − y (opposite to the direction + y of the imposing current). Alternate Solution: Since hatwide E × hatwide B = hatwide S and the right-hand rule, then hatwide E P is in the − y direction. 004 (part 1 of 5) 10.0 points Consider a monochromatic electromagnetic plane wave propagating in the z direction. At a particular point in space, the magnitude of the electric field has an instantaneous value of 222 V / m in the positive x-direction. The wave is traveling in the positive z-direction. ragsdale (zdr82) – HW10 – ditmire – (58335) 2 z x y E wave propagation The speed of light is 2 . 99792 × 10 8 m / s, the permeability of free space is 4 π × 10 − 7 T · N / A and the permittivity of free space 8 . 85419 × 10 − 12 C 2 / N · m 2 ....
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This note was uploaded on 11/03/2010 for the course PHYSICS 303 taught by Professor Shih during the Spring '10 term at University of Texas.
- Spring '10