1. Electric Current
Chapter 34

2. Flow of Charge Heat Flow
Heat flows from higher temperature end to lower temperature end
Heat flow ceases when both ends reach the same temperature

3. Flow of Charge Charge Flow
Charge flows from one end to another when there is a potential difference
When there is no potential difference, there is no longer a flow of charge

4. Voltage Sources An electric “pump” is needed for potential difference
The potential energy per coulomb of charge is the voltage
Voltage is the “electric pressure” to move e- between terminals

5. Voltage Sources (con’t.)
Generators
convert mechanical energy to electrical energy
example: alternator in automobiles
Wet/Dry Cells
energy released in a chemical reaction is converted to electrical energy

6. Electric Current Unit for Charge
Coulomb = the charge of 6.25 X 1018 electrons

7. Electric Current Current (I) Flow of charge Unit: ampere (amp)
Flow of one coulomb of charge per second
Unit: ampere (amp)
Given : 15 amps = How many electrons each second?

8. Electric Resistance Resistance (R) Resistance to flow Unit: ohm ()
Dependent on material used in wire, temperature (greater in higher), length (less in shorter), and thickness (less in thick)

9. Electric Potential Potential Difference
Electric Potential Energy / Charge
Unit: Volts (V)

10. Ohm’s Law
I = V/R
What happens to current, when the voltage is doubled?
What happens to current, when the resistance is doubled?
How much current is drawn by a lamp that has a resistance of 100 ohms with 50 V?

11. Conducting Circuit Material
Source of Electrons
Conducting Circuit Material
electrons do not come from voltage source; voltage source provides the energy
electrons vibrate to and from fixed positions

12. Electric Power = (I)( V)
1 Watt = (1 amp) (1 volt)
1 kilowatt = 1000 watts
1 kilowatt - hour = amt. Of energy consumed in 1 hour at the rate of 1 kilowatt

13. Practice Problems
If a circuit has a resistance of 40 ohms and a current of 3 amperes, what is the voltage across the circuit?
A radio that has 360 ohms of resistance is plugged into a typical 120 volt wall outlet. What is the current in the radio?

14. Practice Problems 2
What is the wattage of a bulb in a lamp (on 120 V outlet) that draws .833 amperes?
If you use an average of 550 watts of power in the lights in your house, and they are on an average of 16 hours a day, what is your energy usage for a 30 day month?

15. How our homes are protected from fire – weakest link
Fuses & Circuit breakers