1. Electric Current
13.2

2. Objectives-SWBAT
Describe how voltage difference causes current to flow
Explain how batteries produce a voltage difference in a circuit
List the factors that affect an object’s electrical resistance
Define Ohm’s Law

3. Electric Current
The net movement of electric charges in a single direction is an electric current.
In a metal wire, or any material, electrons are in constant motion in all directions. As a result, there is no net movement of electrons in one direction.
Electric current is measured in amperes (A).

4. Voltage Difference
Just as water flows from high to low pressure, current flows from high voltage to low voltage

5. Voltage Difference
A voltage difference is related to the force that causes electric charges to flow. Voltage difference is measured in volts.

6. Electric Circuits
A closed path that electric current follows is a circuit.
If the circuit is broken by removing the battery, or the lightbulb, or one of the wires, current will not flow.

7. Batteries
To keep an electric current continually flowing in the electric circuit a voltage difference needs to be maintained in the circuit.
A battery can provide the voltage difference that is needed to keep current flowing in a circuit.
Current flows as long as there is a closed path that connects one battery terminal to the other battery terminal.

8. Dry-Cell Batteries
The cell is called a dry cell because the electrolyte is a moist paste, and not a liquid solution.
Examples: AA, AAA Batteries in flashlights

9. Wet-Cell Batteries
A wet cell contains two connected plates made of different metals or metallic compounds in a conducting solution.
Examples: Car Battery

10. Resistance
As the electrons flow through the filament in a lightbulb, they bump into the metal atoms that make up the filament.
In these collisions, some of the electrical energy of the electrons is converted into thermal energy, becoming hot enough to glow.

11. Resistance
Resistance is the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.
Measured in ohms ().
Resistance Increases as
Wire becomes longer
Wire becomes thinner
Wire becomes warmer

12. Current in Simple Circuits
A simple electric circuit contains
A source of voltage difference (Battery)
A device (light bulb) that has resistance,
Conductors that connect the device to the battery terminals.
When the wires are connected to the battery terminals, current flows in the closed path.

13. Ohm’s Law
According to Ohm’s law, the current in a circuit equals the voltage difference divided by the resistance.

14. V I R Ohm’s Law Memory Trick
Hold your thumb over the variable you are trying to find and you will see the formula V R I

15. Ohm’s Law Practice
Calculate the current in a circuit if the resistance of the light bulb is 2 ohms and the battery has a voltage difference of 12 V.
Calculate the current in a circuit if the resistance of the light bulb is 4 ohms and is connected by a 24 V battery.

16. Discussion Questions
__________ is the net movement of electric charges in a single direction.
A. An open circuit
B. Electric current
C. Proton flow
D. Voltage
What is a volt?
What is the tendency for a material to oppose the flow of electrons called?