1. Announcement Ohm’s law video is due at midnight Makeup lab today
No lab tomorrow

2. Why Make Electrons Flow Anyway? 4.2.3A Ohm’s Law & Circuit Basics

3. Ohm’s Law Voltage results in current flow More voltage = more current
Resistance opposes current flow
More resistance = less current

4. Example #1
A potential difference of 25.0 volts is supplied to a circuit with 100 ohms of resistance.
How much current flows through this circuit?
I = V / R
I = 25.0 V / 100 Ω
I = 0.25 A

5. Example #2 A current of 2.0 amperes flows through a 10 ohm resistance.
What voltage must be applied to this resistance?
I = V / R
V = IR
V = (2.0 A)(10 Ω)
V = 20 V

6. Example #3
A 10 volt battery establishes a current of 5.0 amperes in a circuit.
What is the resistance of this circuit?
I = V / R
R = V / I
R = (10 A) / (5.0 A)
R = 2.0 Ω

7. What About
Watts?
4.2.3B Electrical Power

8. Power Law Moving electrons (current) requires ENERGY
How much energy gets used depends on:
Strength of push – VOLTAGE
Rate of flow – CURRENT

9. Example #1
A 12 volt battery is connected to a circuit which allows 10 amperes of current to flow.
What is the power output of this circuit?
P = IV
P = (12 V)(10 A)
P = 120 W

10. Example #2
A 100 watt light bulb is connected to a 120-volt power supply.
What amount of current must pass through the light bulb?
P = IV
100 W = (120 V) I
I = A

11. Example #3
A 2.0 ampere current passes through a circuit with a 300 ohm resistance.
What is the power generated in this circuit?
P = I2 R
P = (2.0 A)2 (300 Ω)
P = 1200 W or 1.2 kW