1. Ohm’s Law
Definition
Whiteboards
An Elaborate Analogy

2. Ohm’s Law V = Voltage (like pressure) I = Current (like flow rate)+ - A R V
R = V I
R = Resistance in ohms ()
V = Voltage in Volts (V) (pressure)
I = Current in Amps (A) (flowrate)

3. Ohm’s Law - The way I think of it
V = Voltage (like pressure)
I = Current (like flowrate)
R = Resistance to flow + - A R V
I = V R
R = Resistance in ohms ()
V = Voltage in Volts (V) (pressure)
I = Current in Amps (A) (flowrate)

4. Ohm’s Law I = V R R = Resistance in ohms ()+ - A R V
I = V R
R = Resistance in ohms ()
V = Voltage in Volts (V) (pressure)
I = Current in Amps (A) (flowrate)
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9
Gold 5%
Silver 10%
No color 20%
Demo - pass around resistors
(two properties - power and resistance)
Demo - power supply, resistor, light bulb
(show increase/decrease V, and R)

5. Ohm’s Law R = V I R = Resistance in ohms ()+ - A
120. mA
12.0 V
R = V I
R = Resistance in ohms ()
V = Voltage in Volts (V) (pressure)
I = Current in Amps (A) (flowrate)
R= ??
Example 1: What is the resistance in the circuit above?
R = V/I = (12.0 V)/(.120 A) = 100. 
Example 2: If there is a 220  resistor in the circuit above, what is the current?
R = V/I, I = V/R = (12.0 V)/(220 ) = = .055 A or 55 mA

6. Whiteboards
1 | 2 | 3 | 4 | 5 | 6

7. What is the resistance of a light bulb if it draws 250 mA of current from a 6.15 V battery? (1000 mA = 1 A)
Given:
R = V I
R = ??
V = 6.15 V
I = .250 A
R = 24.6  W
24.6 

8. What current will flow if you plug a paperclip with a resistance of
What current will flow if you plug a paperclip with a resistance of .065  into a 12 V source?
Given:
R = V I
R = .065 
V = 12 V
I = ??
I = A W
180 A

9. What voltage do you need to push 1
What voltage do you need to push 1.5 Amps of current through a 210 ohm resistor?
Given:
R = V I
R = 210 
V = ??
I = 1.5 A
V = 315 V W
315 V

10. What current flows through an 8
What current flows through an 8.1 ohm speaker when there is a voltage of 3.45 V?
Given:
R = V I
R = 8.1 
V = 3.45 V
I = ??
I =
I = .43 A W
.43 A

11. An unknown resistor draws. 0128 Amps of current from a 23. 9 V source
An unknown resistor draws Amps of current from a 23.9 V source. What is the resistance?
Given:
R = V I
R = ??
V = 23.9 V
I = .0128
R =
R = 1870  W
1870 

12. A 1200 ohm resistor is hooked up to an unknown voltage source, and it draws 87.5 mA of current. What is the voltage?
Given:
R = V I
R = 1200 
V = ??
I = A
V = 105 V W
105 V

13. A 670 ohm resistor is connected to a 1. 5 V battery
A 670 ohm resistor is connected to a 1.5 V battery. What time will it take for 3.0 C of charge to flow from the battery?
Given:
R = V I
I = q t
R = 670 
V = 1.5 V
I = ??
q = 3.0 C
t = ??
t = 1340 s W
1340 s

14. A 3.0 V battery with a capacity of 350 mAh (350 milli amp hours) is drained in 4 hours and 27 minutes. What is the resistance of the circuit that it is attached to?
Given:
R = V I
I = q t
R = ?? 
V = 3.0 V
I = ??
q = (.350e-3)(3600) = 1260 C
t = 4* *60 = s
R =  = 38  W
38 

15. A Cell. + and -, Infinite current, R = 0, what’s really inside
Symbols + -
A Cell. + and -, Infinite current, R = 0, what’s really inside
A Battery of cells
A resistor
A voltmeter, R = infinity V3
An ammeter, R = 0 A3

16. Water in pipes: Electrons in wires:
An analogy
Water in pipes: Electrons in wires:
Flow rate (GPM) Current (Amps = C/s)
Pressure Voltage
Constriction Resistance
Constant P Pump Batteries/Cells
Current convention
Restriction
Wires are superconductors R1 + - A3 R2