1. Resistance

2. What is resistance?
Resistance is the property of a material that resists the flow of charged particles through it.

3. What is resistance measured in?
Resistance is measured in ohms.
The symbol Ω (omega) is used for ohms.

4. What affects resistance?
Conductivity
Better conductors offer less resistance
Temperature
Higher temperatures = higher resistance

5. What affects resistance?
Thickness of the wire
Thin wires have less resistance
Length of the wire
The longer the wire, the more resistance.

6. What is Ohm’s Law?
For a circuit of a given resistance, the current and voltage are proportional.

7. Ohm’s Law formula Current = voltage ÷ resistance
In units: amperes = volts ÷ ohms

8. Associated Formulas Voltage = current x resistance
Resistance = voltage ÷ current

9. Sample Problem One:
A 4V battery is attached to a circuit with 2Ω resistance. What is the current?
Current = voltage ÷ resistance
Current = 4V ÷ 2Ω
Current = 2A

10. Sample Problem Two:
A 5A current is occurring across a 3Ω resistor. What is the voltage?
Voltage = current x resistance
Voltage = 5A x 3Ω
Voltage = 15V

11. Sample Problem Three:
A 20V source is producing 4A of current. What is the resistance?
Resistance = voltage ÷ current
Resistance = 20V ÷ 4A
Resistance = 5Ω