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Electric Circuits. containing resistors. Circuits. Charges travel in a circuit to maintain charge balance. Resistance. Current does not flow unhindered Electrical resistance is analogous to friction or drag Expressed as potential needed to maintain a current. Potential source.
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Electric Circuits containing resistors
Circuits Charges travel in a circuit to maintain charge balance
Resistance • Current does not flow unhindered • Electrical resistance is analogous to friction or drag • Expressed as potential needed to maintain a current
Potential source resistor Circuit Diagrams
Kirchoff’s Laws • Current into any node equals current out of the node I2 I1 I3 I1 = I2 + I30 = I2 + I3 – I1 “Current law” “Junction law” Conservation of charge
Kirchoff’s Laws • Potential drop around any closed loop is zero V1 V – V1 – V2 = 0 V1 + V2 = V V “Voltage law” “Loop law” V2 Conservation of energy
Question: Series Circuit R1 R2 R3 Circuit resistance is A. More than with one bulb.B. Less than with one bulb.C. The same as with one bulb.
Series Circuit R1 R2 R3 Circuit resistance = R1 + R2 + R3
Series Summary • The same current flows through all resistors in series. • The series resistance is the sum of the resistors’ resistances. • The resistors’voltage drops add up to the series total. • The voltage drop across a resistor is proportional to its resistance.
Question: Parallel Circuit Circuit resistance is A. More than with one bulb.B. Less than with one bulb.C. The same as with one bulb.
1 1/R1 + 1/R2 + 1/R3 Currents Total current = I = I1 + I2 + I3 = V/R1 + V/R2 + V/R3 Circuit resistance =V/I =
R = Parallel Summary • The same voltage drops across all resistors in parallel. • The series current is the sum of the resistors’ currents. • The effective resistance is less than for any individual resistor. • Formula is
1 1/R2+ 1/R3 Series and Parallel Circuit Circuit resistance = R1 +
12 W 6 W 9 W 18 W 8 W 9 W 10 W 18 W 9 W 3 W Group Work Determine current direction, current, voltage, and power dissipated for each resistor.
12 W 6 W 9 W 18 W 8 W 9 W 10 W 18 W 9 W 3 W Group Work • Determine the power for each resistor.
Using Kirchoff’s Rules • Make as many loop equations as there are unique loops. • Make as many node equations as there are branches. • The number of equations may depend on how much cleaning up you do beforehand.