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Kirchhoff’s Rules for Complex circuits Sum of voltage changes around a loop is zero Current into any junction must equal the current out of the junction. Complex circuits can’t simplify to one battery and one resistor Reff. Have to use Kirchhoff’s rules to write equations and solve for unknowns. • Guess any direction for any currents…if you’re wrong, that current will be _________ in the solution. • Write equations for as many loops or junctions as you need to find unknowns • As you go along a loop, if you go through a resistor “downstream” (with current) ∆V is _____; if you go “upstream” ∆V is _____. • Use sign on emfs (batteries) to know sign of ∆V as you go through it in either direction. Electrical shock danger Sign near ESC huge pendulum: Caution: 10,000 Ohms! What is it that kills: Current, voltage, or total charge? Smallest you can feel? Enough to kill you? Skin resistance Frequency P1. Write the voltage change equation for the loop we didn’t use in the solution. A. I did it and checked with another classmate B. I did it P2. In circuit I, which bulb puts out more light? A. high R B. low R C. same from each high R high R low R low R P3. In circuit II, which bulb puts out more light? A. high R B. low R C. same from each