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Unformatted text preview: PHYSICS 9C MIDTERM 1 April 24, 2006 Problem 1 . (2 points) Consider two negatively charged particles with Q 1 = -1 C and Q 2 = -2 C. Force between them is: A) Attractive; force on particle 1 is twice larger than force on particle 2. B) Attractive; force on particle 1 is equal to force on particle 2. C) Zero. D) Repulsive, force on particle 1 is twice smaller than force on particle 2. E) Repulsive; force on particle 1 is equal to force on particle 2. Solution: The force is repulsive and the same because it depends on the product of two charges and the distance between them, Answer E. Problem 2 . (2 points) A negative charge Q=- 2 mC is placed inside a spherical conducting shell with the inner radius a and the outer radius b which has an extra charge of 4 mC. Find the charges at the inner and outer surfaces of the shell. Solution. Taking a Gaussian surface inside the conductor Q in +Q=0 therefore Q in =+2mC Charge conservation condition of the conductor tells us that Q in +Q out = Q extra Q out =Q extra-Q in =4 mC-2 mC = 2 mC Problem 3 . (2 points) Find the electric flux through a cubic Gaussian surface of the side a 1 m surrounding a charge of 3 C....
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