1. Current Electricity
Chapter 22
Physics

2. Producing Electric Current
Charges flow from higher potential difference to lower potential differences
Some external source must add in electric energy to the particles
Remember that potential difference is the electrical energy per charge
Electric current = continuous flow of electrons. Static electricity was one big jump of electrons.
Potential difference – other ways of looking at it:
energy available to move electrons
amount of difference in electron density

3. Electric Circuits A closed path for electrons to flow
Direction of flow:
The first electrical scientists thought of current as flowing positive charges (went from + terminals to – terminals) – Conventional Current
Later it was discovered that electrons are the ones that really flow (go from – terminals to + terminals) – Charge Current

4. Electric Power The rate at which electrical work is done P = I * V
P = Power (Watts)
I = Current (Amps or Amperes)
V = Voltage/Potential Difference (V)

5. Electric Power – Problem 1
(p 594 Ex 1) A 6.0 V battery delivers a 0.50 A current to an electric motor connected across its terminals.
What power is delivered to the motor?
If the motor runs for 5.0 min, how much electrical work is done?
3.0 Watts, 9.0 x 102 J

6. Electrical Power – Problem 2
(p 594 #3) What is the current through a 75 Watt lightbulb that is connected to a 125 V outlet?
0.60 Amps

7. Using Electrical Energy
Some electrical energy is always converted to thermal energy
You can calculate how much energy is converted with these equations:
E = P*t
E = I2Rt
Sometimes this is intentional! Like the burner on a stove.

8. Electrical Energy – Problem 1
(p 602 Ex 3) A heater has a resistance of 10.0 Ω. It operates on V.
What is the power dissipated by the heater?
What thermal energy is supplied by the heater in 10.0 s?
1440 Watts, J

9. Electrical Energy – Problem 2
(p 603 # 23) A 15 Ω electric heater operates on a 120 V outlet.
What is the current through the heater?
How much energy is used by the heater in 30.0 s?
How much thermal energy is liberated in this time?
8.0 A, J, J

10. Circuit Diagrams – Symbols to Know
Do not have to copy inductor, potentiometer or electric connections. Add + and – signs to battery

11. Circuit Diagrams Steps:
Draw the battery source to the left. Put the + terminal on top.
Draw the path starting from the + terminal. Make all lines straight and neat.
Make sure that all components are shown with the proper symbol and that the path is complete (ends at the – terminal)
We have to be consistant, so no matter who puts a circuit together from a drawing it looks the same and does the same thing!

12. Two Types of Circuits
Series circuit – has ONE path for electrons to flow
Parallel circuit – has multiple (parallel) paths for electrons to flow
Draw an example of each

13. Parts of a Circuit - 1
Voltmeters – measure the voltage. Must be hooked up in parallel of what you are measuring the voltage across
Ammeters – measure the current. Must be in series.
Fuses – safety device. Small piece of metal with a low melting point that melts when a set current is reached
These are not exclusive, just some of the most common.
Have examples of a fuse, resistor, transistor, led

14. Parts of a Circuit - 2 Resistors – color coding system
4th band is tolerance. (gold
or silver) Put this band to the RIGHT
Let them each try to ID a resistor. Swap with their neighbor.

15. Parts of a Circuit - 3 LED – Light Emitting Diode
Uses less energy and lasts longer
+ (long) goes to – terminal of battery
- (short) goes to + terminal
Transistors – a semiconductor device that uses a small amount of voltage or current to control a larger change in V or I