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Unformatted text preview: howard (cah3459) – oldmidterm 01 – Turner – (56705) 1 This printout should have 19 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points The figure below shows two particles, each with a charge of + Q , that are located at the opposite corners of a square of side d . + + P Q Q d What is the direction of the net electric field at point P ? 1. correct 2. 3. 4. 5. Explanation: At point P , the electric fields due to the two positive charged particles have the same mag nitude. One points downward, and the other horizontally to the left. Thus the direction of the net electric field points left and downward, forming a 45 ◦ angle with the horizontal. 002 (part 2 of 2) 10.0 points What is the potential energy of a particle of charge q that is held at point P ? 1. U = √ 2 2 π * q Q d 2. U = √ 2 4 π * q Q d 3. U = 1 4 π * q Q d 4. U = 0 5. U = 1 2 π * q Q d correct Explanation: The potential energy of the particle charged + q is the sum of the potential energies due to the two + Q charged particles. U = U 1 + U 2 = 1 4 π * q Q d + 1 4 π * q Q d = 1 2 π * q Q d . 003 10.0 points Two spheres, fastened to “pucks”, are rid ing on a frictionless airtrack. Sphere 1 is charged with 1 nC, and sphere 2 is charged with 2 nC. Both objects have the same mass. 1 nC is equal to 1 × 10 9 C. As they repel, 1. sphere 1 accelerates 4 times as fast as sphere 2. 2. they have the same magnitude of acceler ation. correct 3. sphere 1 accelerates 2 times as fast as sphere 2. 4. sphere 2 accelerates 2 times as fast as sphere 1. 5. they do not accelerate at all, but rather separate at constant velocity. 6. sphere 2 accelerates 4 times as fast as sphere 1. Explanation: howard (cah3459) – oldmidterm 01 – Turner – (56705) 2 The force of repulsion exerted on each mass is determined by F = 1 4 π * Q 1 Q 2 r 2 = ma where r is the distance between the centers of the two spheres: + F 12 = + F 21 . Since both spheres have the same mass and are subject to the same force, they have the same acceleration. 004 10.0 points From the electric field vector at a point, one can determine which of the following? I. the electrostatic charge at that point; II. the direction of the electrostatic force on a test charge of known sign at that point; III. the magnitude of the electrostatic force exerted per unit charge on a test charge at that point. 1. I only 2. III only 3. All of these 4. II and III only correct 5. None of these 6. II only 7. I and II only 8. I and III only Explanation: The definition of the electrostatic force is + E = + F q , so + F = q + E and + F acts in the same or opposite direction to + E depending on the sign of the charge. If we only consider the magnitude F = q E for a unit charge, the electric field’s magnitude is E = F q ....
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 Spring '10
 Turner
 Charge, Electric charge, Howard

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