1. Do Now: Which resistor takes a larger current through it?
Which resistor has a larger voltage?
Explain #1 and #2 from your notes!

2. Aim: How do we determine the variables in a parallel circuit?
HW:

3. Conventional Current
The direction that positive charge would flow equal to electron flow.

4. Parallel Circuits
A circuit in which all of the components are connected “in parallel” to the same voltage source, creating MULTIPLE LOOPS.

5. Parallel Circuits
The charges fall through the 30Ω resistor at a slower rate.
Less CURRENT flows through that branch of the circuit!

6. Junction Rule The total current flowing INTO a junction of two or more
wires is the SAME as the total current flowing OUT
of the junction.
10A ? 5A 5A

7. Junction Rule 6A ? ?
10A 6A 4A 2A

8. Rules
The equivalent resistance is the INVERSE OF THE SUM of the INVERSE OF EACH RESISTANCE
The total current in the circuit is equal to the SUM of the CURRENT passing through each resistor.
The voltage is the same for ALL resistors in the circuit.
All COMPONENTS and the WHOLE CIRCUIT obey Ohm’s Law

9. Example
Two identical resistors connected in parallel have an equivalent resistance of 20 ohms. Determine the resistance of each resistor.

10. V I R P R1 R2 R3 Req 30 Ω 60 V R3 = 30 Ω 120W 60 V 2 A 120 W 60 V 2 A
10 Ω
360W
R1 = 30 Ω
60 V

11. Ohm’s Law Rule
Ohm’s Law may only be used if the current “I” and the voltage “V” are experienced by the resistance “R”.
This means we can’t randomly pick a voltage and a resistance from the problem and divide to get current.
We must be sure the voltage we plugged in is actually measured across the resistance we’re considering.

12. V I R P R1
70 Ω R2
60 Ω R3
50 Ω
Req
R3 = 50 Ω
0.05 A
2.5 V
0.036A
0.09W
2.5 V
0.042A
0.11 W
R2 = 60 Ω
2.5 V
0.05A
0.13 W
2.5 V
0.128A
19.62 Ω
0.32W
R1 = 70 Ω
? V

13. SUMMARY Describe the Parallel Circuit rules for…
Voltage
Current
Resistance
Describe the Junction Rule