1. Electric Current
Section 2

2. Current and Voltage Difference
The net movement of electric charges in a single direction is an electric current
Electric current is measure in amperes (A)
One ampere is equal to 6,250 million billion electrons flowing past a point every second
Electric charge will flow where there is a voltage difference
Voltage difference is measured in volts

3. Electric Circuits A path that an electric current follows is a circuit
A circuit path must be closed
If a circuit path is broken, current will not flow
What happens when you flip off a light switch?
The circuit is broken

4. Batteries
To keep electricity flowing, a voltage difference must be maintained
A battery can supply that voltage difference
Dry Cell Battery
Consists of two electrodes surrounded by an electrolyte
The electrolyte allows charge to move from one electrode to another
In a dry cell the electrolyte is not a liquid

5. Batteries Wet Cell Batteries Lead-Acid Batteries
Contain two connected plate made of different metals or metallic compounds in a conducting solution
A wet cell batteries contains many wet cells connected together
Lead-Acid Batteries
Most car batteries
Contains 6 wet cells
Lead and Lead Dioxide plates
Sulfuric Acid solution

6. Resistance
When electrons flow through a material, the material will offer some resistance to the flow of electrons
Resistance is due to collisions of the electrons with atoms in the material it is flowing through
Some of the electrical energy of the electrons is converted to thermal energy
Sometimes the resistance is great enough that it causes the material to glow
Flashlight filaments
Most materials offer some electrical resistance (except super conductors)
Electrical conductors offer less resistance than electrical insulators

7. Resistance Temperature, Length, and Thickness will affect resistance
Resistance tends to increase as temperature increases
Resistance tends to increase as the distance traveled (length of the wire) increases
Resistance tends to increase as the wire becomes thinner
How could you manipulate a metal filament to become more resistant?
Coil the metal to increase length
Use thin wire
Why would you want to?
Filament must glow so resistance must be high

8. The Current in a Simple Circuit
Simple circuit has
A source of voltage difference
battery
A device that has resistance
light bulb
Conductors that connect the device to the battery terminals
wires

9. Ohm’s Law Resistance, current, and voltage difference are related.
The relationship is known as Ohm’s Law
The current in a circuit equals the voltage difference divided by the resistance
Current (in amps) = voltage difference (in volts)
resistance (in ohms)
I = V/R

10. Ohm’s Law
Calculate the voltage difference in a circuit with a resistance of 25 ohms if the current is 0.5A
12.5 Volts

11. Ohm‘s Law
A current of 0.5 A flows in a 60-W bulb when the voltage difference between the ends of the filament are 120 V. What is the resistance of the filament?
240 ohms