1. Aim: How do we explain Parallel Circuits?

2. Parallel Circuits
When resistors are connected in parallel, there are multiple paths for current to flow.

3. Rule #1 for Parallel Circuits
The total current is equal to the sum of the current values in each of the branches. Itotal = I1 + I2 + I3 +…
What is the total current?
14 A

4. Rule # 2 for Parallel Circuits
The potential difference across each resistor in a parallel circuit is equivalent to the potential difference of the voltage source (battery)

5. Rule # 3 for Parallel Circuits
The reciprocal of the equivalent resistance is the sum of the reciprocals of each of the individual resistors. 1/Req =1/R1 +1/R2 +1/R3 +… Find the equivalent resistance of each set of parallel resistors. 1/Req=1/6Ω+1/6Ω+1/6Ω Req=2Ω 1/Req=1/9Ω+1/9Ω+1/9Ω Req=3Ω 1/Req=1/12Ω+1/12Ω+1/12Ω Req=4Ω

6. Parallel Circuit Problem # 1

8. Parallel Circuit Problem # 2
Calculate the following:
The equivalent resistance of the circuit
The total current in the circuit
The voltage drop across the 12 ohm and 4 ohm resistor
The current in both the 12 ohm and 4 ohm resistor

10. Parallel Circuit Thought Question
1. As more and more resistors are added in parallel to a circuit, the equivalent resistance of the circuit ____________ (increases, decreases) and the total current of the circuit ____________ (increases, decreases).

11. Parallel Circuit Thought Question
2. Three identical light bulbs are connected to a D-cell as shown below.
P, Q, X, Y and Z represent locations along the circuit.
Which one of the following statements is true?
The current at Y is greater than the current at Q.
b. The current at Y is greater than the current at P.
c. The current at Y is greater than the current at Z.
d. The current at P is greater than the current at Q.
e. The current at Q is greater than the current at P.
f. The current is the same at all locations.

12. Parallel Circuit Thought Question
3. Three identical light bulbs are connected to a D-cell as shown below. P, Q, X, Y and Z represent locations along the circuit. At which location(s), if any, will the current be ... a... the same as at X? P b. ... the same as at Q? NONE c. ... the same as at Y? Z d. ... less than at Q? Y,Z e. ... less than at P? Q,Y,Z f. ... twice that at Z? Q g. ... three times that at Y? P,X

13. Parallel Circuit Thought Question
4. Which adjustments could be made to the circuit below that would decrease the current in the cell? List all that apply. a. Increase the resistance of bulb X. b. Decrease the resistance of bulb X. c. Increase the resistance of bulb Z. d. Decrease the resistance of bulb Z. e. Increase the voltage of the cell (somehow). f. Decrease the voltage of the cell (somehow). g. Remove bulb Y.