spring_06_exam3_sol_phy2049

spring_06_exam3_sol_phy2049 - PHY2049 Spring 2006 Exam 3...

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PHY2049 Spring 2006 Exam 3 Solutions 1 Prof. Darin Acosta Prof. Greg Stewart April 26, 2006 Exam 3 (Make-up) Solutions 1. An electric dipole is aligned along the z-axis, with the center between the two charges at z=0, the +q charge at z=+d/2, and the –q charge at z= - d/2. In addition , a charge of +q is located on the z-axis at z= - d, i. e. at d/2 below the –q charge. What is the electric field at a point P on the z-axis at z=+100 d from z=0 and the center of the dipole, in units of q/(2 πε 0 d 2 ), due to the dipole plus the point charge? (You may use the approximation for the electric dipole field since the location of point P >>d away from the origin.) a. 50 10 -6 b. 99 10 -6 c. 95 10 -6 d. 10 -6 e. 25 10 -6 Solution: E = (1/2 πε 0 )qd/(100d 3 ) + (1/4 πε 0 )q/(101d 2 ) (q/2 πε 0 ) [1/d 2 ] {10 -6 + 1/(2*101 2 )} = q/(2 πε 0 d 2 ) (10 -6 + 49*10 -6 ) 2. At each point on the surface of the cube shown, the electric field is parallel to the y axis. The length of each edge of the cube is a =5m. Across the left face of the cube ˆ 10 = E y N/C, and across the right face of the cube ˆ 30 = − E y N/C. Determine the net charge contained within the cube in nC (1 nC = 10 -9 C). a. -8.9 b. -4.4 c. 4.4 d. -2.2 e. 6.8 Solution: The electric field points along the y-axis, so the electric flux through a surface, defined by Φ= ⋅ EA , is non-zero only for the left and right faces. For both
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This test prep was uploaded on 04/17/2008 for the course PHY 2054 taught by Professor Avery during the Spring '08 term at University of Florida.

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spring_06_exam3_sol_phy2049 - PHY2049 Spring 2006 Exam 3...

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