Resistance and Ohm's Law

A flow of electrons along a wire

As the electrons move along the wire, they collide with the metal atoms. These collisions make the atoms vibrate more, which makes the metal hotter

Resistance is a measure of how much a material tries to stop electricity from passing through it

All wires and devices have some resistance, which is why electrical appliances always waste some energy as heat

A component designed to reduce the current

It has a resistance that can be changed

It has a resistance that remains the same

• Material

• Thickness

• Temperature

• Length

Some materials allow electricity to flow through easier, such as copper

Increasing thickness decreases resistance

Decreasing temperature decreases resistance

Increasing length increases resistance

A material that conducts electricity with a very low resistance at very low temperatures

It relates current, voltage, and resistance in a three way relationship

Voltage is directly proportional to current. When voltage in a circuit is increased, the current also increases (as long as resistance is constant)

I

Resistance is inversely proportional to current. When resistance decreases in a circuit, current increases (as long as voltage is constant)

V = IR (Voltage equals current times resistance)

Ohm (the symbol is Ω)

Using an ohmmeter

I

Amps

V

Volts

Ω

Ohm’s

Kilo or milli before a unit (A, V, or Ω) is not allowed. You have to convert it to a normal unit. If it has kilo, you times it by 1000. If it has milli, you multiply by 1000