Circuits Series Parallel

V = IR Ohm’s Law V = Voltage (Volts) I = Current (Amps) R = Resistance (Ohms)

Series Circuits Have only one path The battery is represented by the escalator which raises the charges to a higher energy level (voltage source). As the charges move through the resistors (represented by the paddle wheels) the charges do work (J/C), and subsequently, lose energy (experience a voltage drop). The charges do more work as they pass through the larger resistor.

By the time each charge makes it back to the battery, it has lost all of the energy given to it by the battery. The sum of the potential drops (voltage drops) is equal to the potential rise (voltage source) from the battery. This demonstrates that a charge can only do as much work as was done on it by the battery.

Series Circuits Vtot = V1 + V2 +… Itot = I1 = I2 = … The sum of the potential drops equals the potential rise of the energy source The current is the same throughout the circuit The total resistance of the circuit (equivalent resistance) is equal to the sum of the individual resistances. Vtot = V1 + V2 +… Itot = I1 = I2 = … Rtot = R1 + R2 + …

Symbols Used in Drawing Circuits

R1 = 2 ohms R2 = 3 ohms R3 = 1 ohm VB = 12 V (voltage source) Find the equivalent resistance of the circuit. Find the current of the circuit Find the voltage drop at each resistor

Draw a circuit that has: 12 volt battery source 3 Ω resistor 2 Ω resistor Calculate the equivalent resistance in the circuit Calculate the current in the circuit Calculate the voltage drop across each resistor

Parallel Circuits

Voltage The potential drops of each branch equal the potential rise of the source. The voltage is the same through each resistor

Current The total current is equal to the sum of the currents in the branches The current can branch into new pathways that can allow different currents per path.

Resistance The total resistance of the parallel circuit is equal to the inverse of the sum of all the inverse resistance combined Straw comparison!!

Parallel Circuits If your voltage source = 12 V, what is the voltage across each resistor (assume they have the same resistance)? What is the voltage across each resistor if all three resistors are different?

Current in Parallel Circuits Current is divided in the branches Resistance of individual resistors determines how much current will flow through it So – essentially, the currents will be different through each of the resistors.

Current in Parallel Circuits 1) Find the equivalent resistance of the circuit 2) Find the total current flowing in the circuit 3) Find the current flowing through each resistor VB = 12 V R1 = 3 Ω R2 = 2 Ω R3 = 1 Ω