7-2: Electric Current

1. Voltage Charges flow from areas of high voltage to areas of low voltage A voltage difference must be present for electrical charges to flow By definition, voltage difference is the push that causes charges to move Measured in volts (V)

2. Circuit A circuit is a closed, conducting path For electric charges to flow, the wire must always be connected in a closed loop, circuit.

3. Electric Current An electric current is the flow of charges through a wire or any conductor Typically, is the flow of electrons Measured in amperes (A)

4. Static Discharge vs Flowing Current Static discharge – charges move from one place to another in a short period of time In order to keep a current flowing, a device must be present that maintains a voltage difference

5. Dry Cell Batteries Typical battery Voltage difference between the positive and negative terminals Moist chemical paste with a solid carbon rod in the middle

5. Dry Cell Batteries

6. Other Sources Wet Cell Battery – two connected plates in a conducting solution Car Battery – six connected plates Wall sockets/electrical outlets

7. 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 () Copper – low resistance Example – light bulb

7. Resistance

8. Factors That Affect Resistance For more efficient energy flow….want a wire with low resistance For low resistance Thick wire Lower temperature Shorter wire

9. Ohm’s Law Increasing resistance causes the current to decrease Decreasing resistance causes the current to increase Current equals the voltage difference divided by the resistance http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html