Series Circuit Current must pass through all resistors
Rules for Series 1.Total (equivalent) resistance is sum of individual resistances. R E =R 1 +R 2 +…+R n 2.Current is the same everywhere in circuit and equals voltage of battery divided by equivalent resistance. I=V/R E and I 1 =I 2 =…=I n 3. Voltage drop across each resistor equals current times value of that resistor. Sum of individual voltage drops equals voltage of battery. V n =IR n and V E =V 1 +V 2 +…+V n
EXAMPLE Find equivalent resistance: Find current: Find voltage drop across each resistor:
Parallel Circuits Current splits between resistors
Rules for Parallel 1.Total resistance is reciprocal of sum of reciprocals of individual resistances. 1.Total current is voltage of battery divided by total resistance. Current through each resistor is voltage of battery divided by individual resistance. Total current is sum of currents in individual branches. 2.Voltage drop across each resistor equals voltage of battery.
EXAMPLE Find equivalent resistance: Find current through each resistor: Check by finding total current:
EXAMPLE 2 (cont’d) Remember voltage drop across each resistor equals voltage of battery because all energy is used up in one resistor that is passed through: