1. Electric Current
Chapter 17

2. Capacitance Ability to store charge
Capacitance = Charge/Potential Difference
C = Q/V

3. Parallel Plate Capacitors
Capacitance = permittivity * Area/Distance
C = ε0A/d

4. Flow of Charge
Heat flows from higher temp to lower temp as long as temp difference
Water flows from high to low potential

5. Flow of Charge Charge Flow
Charge flows when there is a potential difference
When there is no potential difference, there is no longer a flow of charge

6. An electric “pump” is needed for potential difference
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

7. 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

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

9. Electric Current Current - I Flow of charge Unit: ampere (amp)
Flow of one coulomb of charge per second
Unit: ampere (amp)

10. Electric Resistance…is futile
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)

11. Potential Difference (voltage) - V
Electric Potential
Potential Difference (voltage) - V
Electric Potential Energy / Charge
Unit: Volts (V)

12. Ohm’s Law
I = V/R
V = IR
Bicycle analogy
No new chain created

13. Electric Power P = 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

14. 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?

15. Practice Problems 2
What is the wattage in the 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?

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