Principles of Physics

 More than one resistor in multiple paths  Electrons may go through any path  More electrons will go through path with less resistance  Overall resistance goes down because more than one electron can get through at once Figure 3 R1R1 R2R2

One connection between resistors Two connections between resistors

 Current flow is different in each path depending on the individual resistance I 1 = V 1 /R 1  Total current (current leaving or entering the voltage supply) depends on total resistance I T = V T /R T  Current in all paths add up to the total current leaving the supply I T = I 1 + I 2 + … Figure 3 R1R1 R2R2

 Voltage gained by electrons when leaving the voltage supply equals the voltage lost before returning  Since each electron takes a separate path it must lose all of its voltage through the resistor in that path V T = V 1 = V 2 = … Figure 3 R1R1 R2R2

To determine the current leaving the voltage supply the total resistance must be used 1 R T = … R 1 R 2 Figure 3 R1R1 R2R2

Determine the total resistance in the circuit at left if R 1 = 6 Ω and R 2 = 6 Ω 1 R T = R 1 R 2 1 R T = R T = = R T = 3 Ω Figure 3 R1R1 R2R2

Determine the total resistance of the circuit. 1 R T = R 1 R 2 1 R T = R T = = 0.5 R T = 2 Ω Figure 3 4 Ω 12 V

Determine the total current of the circuit. V = IR 12 = I(2) I = 6 A Figure 3 4 Ω 12 V

Determine the current through each of the resistors V = IR 12 = I(4 ) I = 3 A Figure 3 4 Ω 12 V

 Adding a resistor in parallel decreases the overall resistance  Total resistance will be less than any of the individual resistors  When one resistor is disconnected only that path is open – current flows in the rest of the circuit (light bulbs will stay lit)  Everyone picks one door to get out  Most will go through largest door