• What are the 4 main components of a circuit?• List and give examples

Topic 3: Resisting the Movement of Charge

Review: Voltage (a.k.a. Potential Difference)• Voltage is the electric pressure, or force,

that causes electrons to move.• Measured in Volts (V)• Examples:

• Your house receives 120V from the city; • A car requires 12V;• A flashlight requires 1.5V

• Sources of voltage: batteries, generators

Review: Current

• Current is the rate or speed of electron flow• Measured in Amperes (I)

Resistance• Resistance is a property of a substance that reduces or

prevents the flow of electric charge.• Resistance causes electric energy to be converted into some

other form of energy, often heat or light.• Resistance is measured in Ohms (Ω)

What might the properties of a tungsten filament be?

Tungsten filament

• Tungsten is a metal so it is a conductor, but it provides a lot of resistance to the flow of electrons compared to other metals.

• Much of the energy of the electrical current is converted to light and heat energy.

Conductors

• A good conductor, like copper, allows electrical charge to flow easily through it. Good conductors have low resistance.

• A poor conductor, like tungsten, opposes or reduces the movement of charge. Poor conductors have high resistance.

Factors Affecting Wire ResistanceFactor EffectLength Resistance increases with length. If the length

doubles, the resistance doublesCross-sectionalarea

Resistance decreases with area. If the cross-sectional area doubles, the resistance is half as great.

Temperature As the temperature of the wire increases, the resistance increases

Material Due to the structure of their atoms, some metals allow electrons to move more freely than others

Voltage, current, and resistance

• Voltage, current, and resistance are all related• Given voltage and current, we can calculate resistance using the

formula:

Example 1

• What is the resistance of an electric heater if a current of 12.5 A runs through it when it is connected to a 120 V wall outlet?

• Solution: R = V/I • R = 120/12.5A• R = 9.60 Ω

You Try!

• What is the resistance of an electric motor if the battery supplies 12 V and the current is 45 amps?

Example 2

• A 1.5 V flashlight has 0.5 Ω of resistance. What is the current through the flashlight?

• Solution: I = V/R• I = 1.5 V/0.5 Ω• I = 3 Amps

You Try!

• The filament of a 3.7 V light bulb has a resistance of 1.8 Ω. What is the current passing through the light bulb?

Practice Problems

• Pg. 282 Questions 1-4• Pg. 291 Questions 7-8

Then take a brain break!!

Series Circuits• Series circuits have only one

current path. • All the moving charges travel

through each component in the circuit.

• Christmas tree lights – if one goes out then they all go out.

Parallel Circuits• Parallel circuits have more than

one current path• The total current is divided,

with some of the moving charges travelling through each branch, or part of a circuit.

House Wiring – Series or Parallel?

Microcircuits – Mother boards on computers