Resistance What is resistance Resistance is the property

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 4 V battery is attached to a circuit with 2Ω resistance. What is the current? • Current = voltage ÷ resistance • Current = 4 V ÷ 2Ω • Current = 2 A

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

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