Electric Current 13.2

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

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).

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

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

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.

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.

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

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

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.

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

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.

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

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

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.

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?