1. Resistance

2. What is a resistor?
A resistor is an object that slows down the flow of electrons and changes electrical energy into a different form
Imagine construction on the highway forcing all the cars into one lane
The construction is the resistor and the cars are electrons

3. The filament of a lightbulb resists the flow of electrons, slowing down the electrons and transforming the electrical energy into light energy
Wires connecting a lightbulb to a battery have very little resistance, so the electrons travelling through the wire lose almost no electrical energy

4. Voltage
Voltage is the difference in potential energy of a charge between one point and another point in the circuit.
If you increase voltage you also increase current
Consider two circuits with the same voltage. One has large resistance (A), and the other has small resistance (B). Which do you think will have the larger current?

5. B has the larger current

6. Ohm’s law
If you know the current and the voltage of a circuit you can calculate the resistance using “Ohm’s Law”:
R=V/I
(sometimes written in the form V = IR)
Resistance is measured in ohms

7. What is the resistance of a flashlight bulb if there is a current of 0
What is the resistance of a flashlight bulb if there is a current of 0.75 A through the bulb when connected to a 3.0 V battery?

8. R = V/I R = 3.0/0.75 R = 4.0 Ω

9. Try the following questions
The current through a load in a circuit is 1.5A. If the potential difference across the load is 12V, what is the resistance?
The resistance of a car headlight is 15Ω. If there is a current of 0.80 A through the headlight, what is the voltage across the headlight?
A 60V potential difference is measured across a load that has a resistance of 15Ω. What is the current through this load?

10. Answers
8.0 Ω
12 V
4.0 A