Midterm2

# Midterm2 - PHYSICS 7b MIDTERM 2 Prof C F McKee Nov 2 2009...

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PHYSICS 7b MIDTERM 2 Prof. C. F. McKee Nov 2, 2009 Partial credit will be given, so show your reasoning carefully. The number of points for each problem is listed at the left. You are permitted one 3x5 card of notes, written on both sides. Relevant constants are given at the end. 1. [10] A D battery that costs \$1.70 delivers 25 mA at 1.5 V for 820 hr. What is the ratio of the cost of this power to that from the 120 V power we get from the wall socket, at \$0.10 per kwh? 2. [15] (Giancoli 23-15.) Consider two conducting spheres, of radius r 1 and r 2 . The spheres are separated by a distance much greater than the size of either one. Initially, the ﬁrst sphere has a charge Q and the second one is uncharged. The two are then connected by a conducting wire. What is the charge on the second sphere once a steady state is reached? 3. [15] An electron is ﬁred through a tiny hole into a capacitor at a velocity of 10 7 m s - 1 . The capacitor is charged so that the ﬁeld inside is E = 2 . 6 × 10

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Midterm2 - PHYSICS 7b MIDTERM 2 Prof C F McKee Nov 2 2009...

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