1. Announcement
Next Exam will be on the Thursday when we get back from break
The EM Exam will be ALL free response
Review materials are posted and you will have Friday’s class to ask any questions
Parallel Circuits Homework is due Thursday

2. Wiring for Voltage
Parallel Circuits

3. Definitions
parallel circuit – a circuit in which two or more elements are connected so that each has its own current loop.

4. Parallel Circuit Rules
equivalent Resistance –> more resistors = less resistance
1/Req = 1/R1 + 1/R2 + …
current – currents add up
I = I1 + I2 + …
voltage – voltages same for each resistor
V = V1 = V2 = …
All circuit components and the circuit as a whole must obey Ohm’s Law

5. Junction Rule
The total current flowing into and out of a junction must be the same
10 A
6.0 A ?
4.0 A

6. Junction Rule
6.0 A
10 A
6.0 A ? ?
4.0 A
2.0 A

7. R1 = 30 Ω
R2 = 30 Ω
R3 = 30 Ω
60 V
V (V)
I (A)
R (Ω) R1 R2 R3
Req 60
2.0 30 60
2.0 30 60
2.0 30 60
6.0 10

8. R1 = 20 Ω
R2 = 50 Ω
R3 = 10 Ω
0.5 A
V (V)
I (A)
R (Ω) R1 R2 R3
Req
5.0
0.25 20
5.0
0.1 50
5.0
0.5 10
5.0
0.85
5.9