2049_ch24b - ConcepTest: Electric Potential Which point has...

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PHY2049: Chapter 24 23 ConcepTest: Electric Potential Î Which point has the largest potential when Q > 0? Î Which two points have the same potential? ± (a) A and C ± (b) B and E ± (c) B and D ± (d) C and D ± (e) no pair A C B D E Q E Smallest radius Same radius
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PHY2049: Chapter 24 24 Multiple Charges: Superposition Î 3 charges: Find total potential at a point in space Q 3 + Q 1 + Q 2 x r 1 r 3 r 2 3 12 123 3 tot Q QQ VV V V k k k rr r =+ + = + + ± V is a scalar ¾ No directions to worry about! ¾ But you do have to watch signs! +Q 1 +Q 2 Q 3
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PHY2049: Chapter 24 25 ConcepTest: Electric Potential Î What is V at point A? ± (a) V > 0 ± (b) V = 0 ± (c) V < 0 Î What is V at point B? ± (a) V > 0 ± (b) V = 0 ± (c) V < 0 Closer to + charge Equal distance to both charges A B Q 2 = +50 μ C Q 1 = 50 μ C 30 cm 26 cm 26 cm 40 cm 60 cm
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PHY2049: Chapter 24 26 ConcepTest: Electric Potential Î At which point does V = 0? ± (a) C ± (b) A ± (c) D ± (d) B ± (e) all of the above A C B D + Q Q All points equidistant from charges
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PHY2049: Chapter 24 27 ConcepTest: Electric Potential Î Which configuration gives V = 0 at all points on x axis? ± (a) A ± (b) B ± (c) C ± (d) All of the above ± (e) None of the above A x +2 μ C -2 μ C +1 μ C -1 μ C B x +2 μ C -1 μ C +1 μ C -2 μ C C x +2 μ C -1 μ C -2 μ C +1 μ C All points on x axis equidistant from each pair of charges
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PHY2049: Chapter 24 28 ConcepTest: Fields & Potentials Î Find E and V at the center of the square. ± (a) E = 0 V = 0 ± (b) E = 0 V 0 ± (c) E 0V 0 ± (d) E = 0 ± (e) E = V regardless of the value -Q -Q +Q +Q
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PHY2049: Chapter 24 29 ConcepTest: Electric Potential Î You move a positive charge Q from A to B along the path shown. What is the sign of the work done by you? ± (a) W AB < 0 ± (b) W AB = 0 ± (c) W AB > 0 A B No change in potential since distance from center is the same
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PHY2049: Chapter 24 30 Potential of Charge Distribution Î Generalize superposition to continuous distribution Î Distribution can be any shape ± Line, surface, volume Î Express dq in terms of charge density ± Line or arc: dq = λ
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2049_ch24b - ConcepTest: Electric Potential Which point has...

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