solutions to test 2 spring 2008

# solutions to test 2 spring 2008 - Physics 2306 Spring 2008...

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Physics 2306 Spring 2008 Second Exam FORM A 1) The electric field lines of two charges, A and B, are shown in the figure. The magnitude of charge A is 12.0 C. What is the charge (in Coulombs) of B? A. 10 B. 10 C. 4.0 D. 4.0 E. 8.0 F. 8.0 G. 20 H. 20 2) A positive point charge q is at (x = 1.0, y = 0, z = 0). A negative point charge q is (x = 0, y = 1.0, z = 0). Which picture below correctly shows the direction of the electric field at the origin? 3) A point charge q = 2.0E-06 C is at the coordinates (x = 0.2, y = 0.1 m, z = 0.2 m). In that coordinate system, what is the magnitude of the electric field (in Newtons/Coulomb) at the origin (x = 0, y = 0, z = 0)? A. 4.0E+05 B. 2.0E+05 C. 3.5E+05 D. 8.0E+05 E. 4.0E+04 F. 8.0E+04 G. 2.0E+04 H. 6.0E+04 A B A x y F x y B x y C x y D x y E x y E = kq/r 2 where r 2 = (0.2) 2 + (0.1) 2 + (0.2) 2

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4) An electric charge q = 5.0E-06 C is placed in an electric field E = 3.0E+06 N/C i 2.0E+06 N/C k . What is the z-component of force (in Newtons) on the charge q? A. 10 B. 10 C. 4.0E+11 D. 4 0E+11 E. 6.0E+11 F. 6.0E+11 G. 15 H. 15 5) Two infinite lines of charge are parallel to the x-axis. One line of charge goes through the point (x = 0, y = a, z = 0) and the other line of charge goes through the point (x = 0, y = a, z = 0). The charge density of the line going through (x = 0, y = a, z = 0) is λ C/m and the charge density of the line going through (x = 0, y = a, z = 0) is λ C/m. What is the electric field (in Newtons/Coulomb) at the origin (x = 0, y = 0, z = 0)? A. (k λ /a) j B. (k λ /a) j C. (2k λ /a) j D. (2k λ /a) j E. (k λ /2a) j F. (k λ /2a) j G. (4k λ /a) j H. (4k λ /a) j 6) A point charge q hangs by a nylon thread from the ceiling. A point charge q also hangs by a nylon thread from the ceiling. The length of each thread is L. The distance between where the threads are attached to the ceiling is 2L. The mass of each point charge is m. The threads each make an angle θ with a line perpendicular to the ceiling as shown in the figure below. What is the transcendental equation for finding the angle θ ? Assume the acceleration of gravity is in the negative z-direction and that the magnitude of the acceleration of gravity is g. A. tan( θ )[1 sin( θ )] 2 = kq 2 /4L 2 mg B. tan( θ ) sin( θ ) 2 = kq 2 /4L 2 mg C. tan( θ )[1 sin( θ )] 2 = kq 2 /L 2 mg D. tan( θ ) sin( θ ) 2 = kq 2 /L 2 mg F = q E F z = ( 5.0E-06 C)( 2.0E+06 N/C) y z λ λ E due to λ E due to λ E Total = E due to λ + E due to λ E Total = 2(2k λ /a) j q q θ θ L L 2L
E. tan( θ )/[1 sin( θ )] 2 = kq 2 /4L 2 mg F. tan( θ )/sin( θ ) 2 = kq 2 /4L 2 mg G. tan( θ )/[1 sin( θ )] 2 = kq 2 /L 2 mg H. tan( θ )/sin( θ ) 2 = kq 2 /L 2 mg 7) A positive point charge q is placed on an infinite sheet of charge. The mass of the point charge is m. The charge density of the sheet is σ . What is the speed of the point charge when it is a distance h above the sheet. Assume the acceleration of gravity is in

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solutions to test 2 spring 2008 - Physics 2306 Spring 2008...

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