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PHY122_L07

# PHY122_L07 - PHY122 Physics for the Life Sciences II PHY122...

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PHY122 PHY122 – Physics for the Life Sciences Physics for the Life Sciences II II PHY122 Physics for the Life Sciences Lecture 7 Currents and Resistance Note: Clicker Channel 21 09/20/2011 1 Lecture 7

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Summary: Currents A l fl h fl n Analogy: water flow = charge flow = electrical current: Q I t current flows from high electrical potential to lower potential charge can be “ pumped up ” inside an emf charge can be stored in a capacitor Kirchhoff’s junction law: in an electrical junction the total flow is conserved : , the the current that goes in = the current that comes out With convention in-going current is positive, out-going current is negative: junction 0 i i I Kirchhoff’s loop law is equally intuitive: in any closed loop , the sum of all potential steps is zer 2 3 0 V V V V V V         steps is zero … closed loop 0 i i V 1 7 6 5 4 7 5 4 3 0 V V V V     1 2 3 4 5 6 1 2 7 6 0 V V V V     Note: signs of Δ V i depend on the direction ! 09/20/2011 2 Lecture 7