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Unformatted text preview: Anderson, Matthew – Homework 4 – Due: Feb 19 2008, noon – Inst: Vitaly 1 This printout should have 18 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 3) 10 points An electric field of magnitude 3230 N / C is applied along the x axis. Calculate the electric flux through a rect angular plane 0 . 431 m wide and 0 . 54 m long if the plane is parallel to the yz plane. Correct answer: 751 . 75 N · m 2 / C. Explanation: Let : E = 3230 N / C , θ = 0 ◦ , L = 0 . 54 m , and W = 0 . 431 m . The area of the rectangle is A = LW = (0 . 54 m)(0 . 431 m) = 0 . 23274 m 2 . Since the field is uniform,the flux is φ = E · A = E A cos θ = (3230 N / C)(0 . 23274 m 2 )(cos0 ◦ ) = 751 . 75 N · m 2 / C . 002 (part 2 of 3) 10 points Calculate the electric flux through the same rectangle, if it is parallel to the xy plane. Correct answer: 0 N · m 2 / C. Explanation: The angle is θ = 90 ◦ ,cos θ = 0 , and φ = E · A = E A cos θ = (3230 N / C)(0 . 23274 m 2 )(0) = 0 N · m 2 / C . 003 (part 3 of 3) 10 points Calculate the electric flux through the same rectangle, but now the rectangle contains the y axis and its normal makes an angle of 21 ◦ with the x axis. Correct answer: 701 . 819 N · m 2 / C. Explanation: Let θ = 21 ◦ φ = E · A = E A cos θ = (3230 N / C)(0 . 23274 m 2 )(cos21 ◦ ) = 701 . 819 N · m 2 / C . keywords: 004 (part 1 of 1) 10 points The net electric flux through a closed surface is 1. infinite only if there are no charges en closed by the surface. 2. zero if only positive charges are enclosed by the surface. 3. zero if the net charge enclosed by the surface is zero. correct 4. zero if only negative charges are enclosed by the surface. 5. infinite only if the net charge enclosed by the surface if zero. Explanation: Gauss’s law tells us the net electric flux through a closed surface is Z s ~ E · d ~ A = Q ² . So the net flux is zero only if the net charge enclosed is also zero....
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This note was uploaded on 03/11/2010 for the course PHYS 121 taught by Professor Opyrchal during the Spring '08 term at NJIT.
 Spring '08
 Opyrchal
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