quiz2solns

quiz2solns - Physics 1B: Electricity & Magnetism Summer...

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Summer Session I, 2010 Quiz #2, July 8, 2010 This is version A ! 1. At all points on the surface of a spherical volume of radius 0.6 m, there is an electric Feld of intensity 100 N/C directed radially outward. What is the net charge enclosed within this volume? a. 0.32 nC b. 4.0 nC c. 6.7 nC d. 24.0 nC e. 66.7 nC We can use Gauss’s Law, Φ E = Q encl 0 , but Frst we need to calculate Φ E , which in this case can be calculated as just EA since the electric Feld lines are perpendicular to the surface. Φ E = EA = E 4 πr 2 = (100 N/C )(4 π (0 . 6 m ) 2 ) = 452 Nm 2 /C . ±rom Gauss’ Law, Q encl = Φ E ǫ 0 = ( E 4 πr 2 ) ǫ 0 = (100 N/C )(4 π (0 . 6 m ) 2 )(8 . 85 × 10 - 12 C 2 N - 1 m - 2 ) = 4 . 0 × 10 - 9 C = 4.0 nC . 2. When charge Q 1 is placed at point P 1 , the resulting potential at point X is V 1 . Then, when Q 2 is placed at point P 2 , the resulting potential at point X becomes V 2 . What is the potential at point X if charge Q 1 is then removed? a. V 2 /2 b. V 1 – V 2 c. V 2 – V 1 d. (V 1 + V 2 )/2 e. V 2 The total potential at any point in space is due to the sum of the potentials from each charge. The answer is V 2 – V 1 , as the potential due to only Q 1 (V 1 ) plus the potential due to only Q 2 (V 2 – V 1 ) equals the potential due to both (V 2 ). 1
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3. Consider a uniform electric Feld of 500 N/C pointing in the +x direction. You wish to move the nucleus of a single ionized carbon atom (12 protons, 12 neutrons) a distance of 10 cm in the –x direction. How much work do you need to provide? a.
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This note was uploaded on 09/13/2010 for the course PHYS PHYS 1B taught by Professor Berman during the Summer '09 term at UCSD.

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quiz2solns - Physics 1B: Electricity & Magnetism Summer...

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