1. Section 2: Electric Current
This section discusses electrical pressure
Charges flow from high voltage areas to low voltage areas
Voltage—like an electrical pressure that pushes charge

2. (Section 2 cont’d)
Just as water or air must have a pressure difference to flow, voltage difference must be present for electric charges to flow
Voltage difference—the push that causes charges to move and is measured in volts (V)
(fig. 11 pg. 202)

3. Closed Circuits
The flow of charges through a wire or any conductor is called electric current
The electric current in a circuit is measured in amperes (A)
Circuit—a closed, conducting path for the flow of electrons

4. (Section 2 cont’d.) Current is almost always the flow of electrons
In order to keep current moving continuously through a circuit a power source (voltage source) is needed
One common source--battery

5. Dry-Cell Batteries
Individual batteries used in flashlights, etc.—dry cell batteries
Made of a zinc container that surrounds a moist chemical paste w/a solid carbon rod suspended in the middle
Provides a voltage difference between +/- terminals

6. (Dry-cell batteries cont’d)
When the two terminals of a dry cell battery are connected in a circuit, a reaction occurs.
The voltage difference between these 2 terminals causes current to flow through a closed circuit

7. Wet-cell batteries
Wet-cell battery—contains two connected plates made of different metals or metallic compounds in a conducting solution
Ex: car batteries (lead plates in sulfuric acid)
The chemical reaction in ea/cell provides a voltage difference

8. More on Batteries
In addition to batteries a voltage difference is provided at electrical outlets
Household devices are designed for 120 V (standard)
Some wall sockets supply 240 V
Ex: electric ranges, clothes dryers, etc.

9. Resistance
Resistance—the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light
All materials have some resistance
Resistance is measured in ohms
*type of material & wire size effect resistance

10. Controlling the flow of electricity
So far: Voltage difference causes charges to flow
An electrical resistance restricts the movement of charges
ex: water flowing in a pipe

11. Ohm’s Law: Current = Voltage difference / resistance OR
I(A) = V (V) / R (ohms)
V = I R
Ohm’s Law Diagram—pg. 207