1. Current Electricity and Circuits
Reference Chapters 34 and 35

2. Flow of Charge
When ends of a conductor are at different potentials, a charge will flow from high potential to low potential until both ends reach a common potential.
When there is no difference, flow ceases.
To sustain flow, a method must be present that maintains a difference much as a water system maintains flow using a pump.

3. Electric Current Flow of charge Carried by electrons in the wire
Carried by anions and cations in electrolytes
Measured in Amperes, coulombs per second
Causes no net charge in a wire

4. Voltage Sources Provides a potential difference in a circuit
Can be batteries(chemical to electrical) or generators(mechanical to electrical)
Can be AC or DC
Electrical potential energy per coulomb is voltage(or electromotive potential or emf)
Unit is volt
Household voltage is 120V AC
Voltage causes current.

5. Electric Resistance Charge depends on voltage and resistance to flow
Resistance depends on resistivity, length, cross-sectional area of conductor and temperature
Resistors are color coded to tell their resistance.

6. Ohm’s Law Current = Voltage/Resistance
For a given amount of current, voltage and resistance are proportional.
The damaging effects of shock are caused by current. The body resistance ranges from 100 when wet to 500,000 when dry.
0.001 A can be felt; A can be fatal.

7. Direct Current and Alternating Current
Refers to direction of flow of electrons
DC only one way, from negative to positive
AC changes directions many times per second depending upon the frequency
AC can be transmitted over great distances with little loss
Converters change AC to DC using a transformer( to lower voltage), a diode(a one way “valve”), and a capacitor

8. The Speed of Electrons in a Circuit
Appear to flow at infinite speed
Really flow at an average of a few million kilometers per hour
Motion is random so not all that productive
Electric field must be present to induce a flow
Field lines are maintained in one direction in a conductor
Electrons bump into metallic ions and transfer some kinetic energy to them causing the wire to become hot

9. The Speed of Electrons in a Circuit
In AC circuit, electrons oscillate about relatively fixed positions.
Nearly speed of light.
Electrons do not flow out of the wall into an appliance; energy does.
Energy is carried by the field and causes vibrations.

10. Electric Power
Rate at which electrical energy is converted into other forms of energy
Power = current x voltage
P = IV
P = I x (IR) = I2R
P = (V/R) x V = V2/ R
Unit is watt or kilowatt

11. Electric Circuits
Path along which electrons can flow from negative to positive
Series circuits – only one path
Parallel circuits – more than one path

12. Series Circuit

13. Series Circuits Current stays the same through all resistors.
I1 = I2 = I3…..
Voltage is used by each resistor individually and is said to “drop” as it passes through the resistor.
VT = V1 + V2 + V3…..
Resistance is unique to the resistor whether it is a lamp, an iron, a toaster or some other device.
Req = R1 + R2 + R3…..

14. Series Circuits Schematics

15. Parallel Circuit

16. Parallel Circuits Current splits among all branches.
IT = I1 + I2 + I3 +…..
Voltage is the same through all branches.
V1 = V2 = V3 =…..
Resistances combine into an equivalent resistance.
1/RT = 1/R /R /R3 +…..

17. Parallel Circuits Schematics