Electric Current and Electrical Energy Unit 10 Section 2

Electric Current An electric current is the flow of electrons through wires. (Just like water flowing through pipes) The higher the current is, the greater the number of charges that pass the point each second. Electric current is expressed in “amperes.” i. The symbol for amp is “A.” ii. The symbol for current is “I.”

Electric Current Electrons moving in a wire make up a current and provide energy. Energy is passed from one electron to another, sort of like when a message is passed from one neuron to another in your body.

Types of Currents There are two kinds of currents: AC-alternating current; the charges continually shift from flowing in one direction to flowing in the reverse. i. This is the current in your home. http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html

b. DC-direct current; the charges always flow in the same direction. i. This is the current in batteries.

Student Extras http://www.physicsclassroom.com/class/circuits/u9l2c.cfm http://education.jlab.org/qa/electron_01.html http://www.kids-science-experiments.com/risingtissuepaper.html

Voltage Voltage is the potential difference between two points on a circuit. i. It is expressed in volts or V. Voltage is a measure of how much work is needed to move a charge between two points. The higher the voltage, the more energy that is released per charge.

Resistance The opposition to the flow of electric charge. Think of resistance as “electrical friction.” Resistance is expressed in ohms (Ω). Good conductors (metal) have low resistance. Poor conductors (rubber and cloth) have high resistance. The higher the temperature, the more resistance.

Resistance and Wire Size A thick, long wire increases resistance. h. A thin, short wire decreases resistance.

Cells a. A cell is a device that produces an electrical current by converting chemical energy to electrical energy. b. There are wet and dry cells. i. Wet cells have liquids in them (like in automobile batteries.) ii. Dry cells have a material in them that is solid or paste-like (cell phone, I-pod)

Photocells c. A photocell is a device that converts light energy to electrical energy. d. An example of a photocell is the dark strip on a calculator that absorbs light from the sun and converts it to electrical energy.

Quickie Quiz 1. The opposition to the flow of charge is: Electric current Voltage Resistance cell

Quickie Quiz 3. Which of the following factors affects the resistance of an object? Thickness of the object Length of the object Temperature of the object All of the above

Quickie Quiz 4. What is the difference between direct current and alternating current?

Quickie Quiz 5. A device that changes chemical energy to electrical energy is a: Superconductor Cell Photocell Thermocouple