Resistance
What is resistance? Resistance is the property of a material that resists the flow of charged particles through it.
What is resistance measured in? Resistance is measured in ohms. The symbol Ω (omega) is used for ohms.
What affects resistance? Conductivity Better conductors offer less resistance Temperature Higher temperatures = higher resistance
What affects resistance? Thickness of the wire Thin wires have less resistance Length of the wire The longer the wire, the more resistance.
What is Ohm’s Law? For a circuit of a given resistance, the current and voltage are proportional.
Ohm’s Law formula Current = voltage ÷ resistance In units: amperes = volts ÷ ohms
Associated Formulas Voltage = current x resistance Resistance = voltage ÷ current
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
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
Sample Problem Three: A 20V source is producing 4A of current. What is the resistance? Resistance = voltage ÷ current Resistance = 20V ÷ 4A Resistance = 5Ω