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Phys 299 Quiz 1 ch 20 solns 2010

# Phys 299 Quiz 1 ch 20 solns 2010 - charge is placed as...

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Solution Phys 299 Quiz 1 chapter 20 Summer 2010 Q.1. If one bag contains a charge 8Q and another one contains charge Q, the 8Q-bag exerts 8 times as much force on the Q-bag as the Q-bag exerts on the 8Q-bag. A) True B) False Q.2. A plastic rod is charged up by rubbing a wool cloth, and brought near an initially neutral isolated metallic sphere. It is allowed to touch the sphere for a few seconds, and then is separated from the sphere by a small distance. After the rod is separated, the rod A) is repelled by the sphere. (because now both are negatively charged because of sharing of excess negative charge) B) feels no force due to the sphere. C) is attracted to the sphere. Q.3. A positive test charge q is released near a positive fixed charge Q. As q moves away from Q, it will move with A) constant velocity. B) decreasing acceleration. (distance increases force decreases) C) increasing acceleration. D) constant acceleration. Q.4. Two equal and opposite charges a certain distance apart are called an electric "dipole". A positive test
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Unformatted text preview: charge is placed as shown, equidistant from the two charges. All three charges are in the plain of the paper. Which diagram below gives the direction of the net force on the positive test charge? A) B) C) D) Q.5. Two charges q 1 and q 2 when separated by a distance r 1 = R produce a force F 1 on each other. If the separation is increased to r 2 = 2R, what is the new force F 2 in terms of F 1 ? A) 4.0 F 1 B) 2.0 F 1 C) 0.25 F 1 D) 0.5 F 1 Soln: F 1 = k q 1 q 2 / R 2 ; F 2 = kq 1 q 2 / (2R) 2 =(1/4)(k q 1 q 2 / R 2 ) = (1/4) F 1 Q.6. An electron experiences a force of 12 mN in the positive x-direction in an electric field. What is the magnitude and direction of the electric field? A) 7.5x10 16 N/C, -x dir B) 5.2x10 19 N/C, -x dir C) 7.5x10 16 N/C, +x dir D) 5.2x10-19 N/C, +x dir Soln: F= e E ; 12x10-3 = (- 1.6x10-19 )E; E = 12x10-3 / (- 1.6x10-19 ) = 7.5x10 16 N/C -x dir...
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