1. Chapter 19: Electric Charges and Currents
19-3: The Flow of Electricity

2. Making Electric Charges Move
You must do work to move a charged particle against an electric field
Unit of Charge: Coulomb (C)
Electric Potential Difference (Voltage): work required per coulomb of charge between 2 points
Units: Volt (V)

3. Battery
Produces electricity by converting chemical energy into electrical energy
Made up of electrochemical cells which are made from materials called electrodes and electrolyte
Electric cells can be dry (paste-like) or wet (liquid) cells

4. Thermocouples Produces electrical energy from thermal energy
Releases electric charges as a result of temperature differences
Used in thermometers in cars to show engine temp.
Engine gets warmer, increases flow of charge, moving charge operate gauge (also in ovens and gas furnaces)

5. Photocells
When light with a certain amount of energy shines on a metal surface, electrons are emitted from the surface, electron routed through a wire to create a constant flow of electric charge

6. Electric Current
Circuit: complete path through which electric charge can flow
Current (I): amount of charge that passes a given point at a given time
Unit of current: Ampere (A)
**Potential Difference is required to produce an electric current**

7. Resistance Resistance (R): opposition of the flow of electric charge
Unit: Ohm (Ω)
- Different wires have different resistances
- All devices have some resistance
- Depends somewhat on temperature: Resistance increases with temperature

8. Ohm’s Law
The current in a wire (I) is equal to the voltage (V) divided by the resistance (R)
Current = Voltage I = V
Resistance R
Amperes = Volts
Ohms

9. Calculating Resistance
In a Series circuit, total resistance is calculated by the equation:
R = R1 + R2 + R3…
In a Parallel circuit, total resistance is calculated by the equation:

10. Series and Parallel Circuits
Series Circuit

11. Current
Direct Current (DC): current flow in the same direction (dry cells and batteries)
Alternating Current (AC): amount of current changes in time and reverses direction regularly
Current in your home changes direction 120 times every second

12. Calculations with Current Electricity
1. There is a 22-ohm resistance in the heating element of a coffee pot. It is plugged into a 110 Volt circuit. How much current passes?
R= 22Ω I = V
V = 110V R
I=? I = 110 V
22 Ω
I = 5 A

13. Calculations with Current Electricity
2. Three lamps with 40,60, and 80 ohms of resistance are connected in parallel to a 120 volt circuit.
a) What current flows through each lamp?
b) What is the total resistance of the 3 lamps?
c) What is the total current used by the 3 lamps?
Given:
V = 120 V
R1=40 Ω R2=60 Ω R3=80 Ω

14. a) What current flows through each lamp?
Lamp 1: I = V/R
I = 120V/40 Ω = 3.0 A
Lamp 2: I = V/R
I = 120V/60 Ω = 2.0A
Lamp 3: I = V/R
I = 120V/80 Ω = 1.5 A

15. b) What is the total resistance of the 3 lamps?
Given: R1=40 Ω R2=60 Ω R3=80 Ω
Since the circuit is in parallel, we use the equation:
1/R1+1/R2+1/R3 = 1/40Ω + 1/60Ω +1/80Ω
= 0.054Ω
Then divide: 1/0.054Ω = 18.5Ω
Total resistance = 18.5Ω

16. c) What is the total current used by the 3 lamps?
Given: V = 120 V RT= 18.5Ω
I = V/RT
I = 120V/18.5Ω
I = 6.5 A