Resistance and Ohm's Law

Getting good study habits

What is electricity?

A flow of electrons along a wire

What happens when electrons move along the 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

What is resistance a measure of?

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

Why do appliances waste energy?

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

What is a resistor?

A component designed to reduce the current

What is a variable resistor?

It has a resistance that can be changed

What is a fixed resistor?

It has a resistance that remains the same

What affects resistance?

• Material

• Thickness

• Temperature

• Length

How does material affect resistance?

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

How does thickness affect resistance?

Increasing thickness decreases resistance

How does temperature affect resistance?

Decreasing temperature decreases resistance

How does length affect resistance?

Increasing length increases resistance

What is a superconductor?

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

What does Ohm’s law relate?

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

When voltage in a circuit is increased, does the current increase or decrease?

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

What is the symbol for current?

I

When resistance decreases in a circuit, does current increase or decrease?

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

What is Ohm’s law?

V = IR (Voltage equals current times resistance)

What is the unit for resistance?

Ohm (the symbol is Ω)

How are ohm’s measured?

Using an ohmmeter

What is the symbol for current?

I

What is the unit for current?

Amps

What is the symbol for voltage?

V

What is the unit for voltage?

Volts

What is the symbol for resistance?

Ω

What is the unit for resistance?

Ohm’s

What happens if you get kiloamps or milliamps or kilovolts of millivolts or milloohms or milliohms?

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