1. Ohm’s Law

2. Electronic Resistance:
Material’s resistance to the flow of electric current
Thin wire
120V
Thick wire
HEAT
LIGHT

3. Ohm’s Equation voltage Current = resistance directly inversely
Current is ________ proportional to voltage
Current is ________ proportional to resistance
inversely

4. Equation: symbol/unitsV I = R
Volts (V)
Amperes (A) =
Ohms (Ω)*
* Ω = OMG

5. Practice #1
How much current will flow through a lamp that has a resistance of 60 Ω when 12V are impressed across it?
voltage
Current =
resistance
12 V
Current = =
0.200 amps
60 Ω

6. Practice #2
What is the resistance of an electric frying pan that draws 12 A when connected to a 120 V circuit?
voltage
Current =
resistance
120 V
12 A = =
10.0 Ω R

7. Resistance in series
2 Ω V I = R
6 V
6 V I =
2 Ω
Current = 3.00 amps

8. Multiple Resistance in series: ADD!
2 Ω V I = R
6 V
6 V I =
2 Ω +
2 Ω
2 Ω
Current = 1.50 amps

9. Resistance in parallel: R equivalent = (R1R2) / (R1+R2)
2 Ω
R = (2x2)/(2+2) =
R = 4/4 =
1 Ω
1 Ω
2 Ω = V I = R
6 V I =
1 Ω
Current = 6.00 A
6 V

10. Series and Parallel: R equivalent = R1R2 / R1+R2
4 Ω
2 Ω =
4 + 2 =
6 Ω
parallel
(6x6) /(6+6) =
6 Ω =
36/12 =
3 Ω V
6 V I I = = R
3 Ω
6 V
Current = 2.00 A
Add series Ω first

11. Series and Parallel: R equivalent = R1R2 / R1+R2
4 Ω
6 Ω
top series
4 + 6 =
10 Ω
inside parallel
(10x10) / (10+10) =
10 Ω
100/20 =
5 Ω
5 Ω =
inside series
5 + 5 =
10 Ω
10 Ω
final parallel
(10x10) / (10+10) =
100/20 =
5 Ω V
6 V I I = =
6 V R
5 Ω
Current = 1.20 A
Work from the inside out

12. More than two Parallel: Solve two at a time!=
top series
4 + 8 =
12 Ω
4 Ω
8 Ω
top two parallel
(4x12) / (4+12) =
48/16 =
3 Ω 4Ω
final parallel
(10x3) / (10+3) =
10 Ω
30/13 =
2.31 Ω V
6 V I I = = R
2.31 Ω
Current = 2.60 A
6 V

13. Parallel Then Series: Current = 2.00 A I Solve parallel first
2 Ω
R = (2x2)/(2+2) =
R = 4/4 =
1 Ω
2 Ω
Series:
1 + 2 = 3 Ω
2 Ω
6 V I =
3 Ω
Current = 2.00 A
6 V
Solve parallel first

14. 1/R equivalent = 1/R1 +1/R2 + …
Alternate equation to calculate resistance.