1. Electric Current and Ohm’s Law

2. Electric Current Electric current is the continuous flow of electric charge Two types of current are direct and alternating Direct current (DC) is when the charge flows in one direction Alternating current (AC) is when the flow of electric charge regularly reverses direction

3. Electric Current An example of a direct current is a flashlight and most battery-operated devices Alternating current is in your home and school Current is defined as the direction in which the positive charges would flow

4. Conductors and Insulators An electrical conductor is a material through which charge can flow easily Metals such as copper, and silver are good electrical conductors An electrical insulator is a material through which charge cannot flow easily Wood, plastic, rubber and air are good electrical insulators

5. Resistance Resistance is the opposition to the flow of charges in a material The SI unit of resistance is the ohm A material’s thickness, length and temperature affect its resistance Resistance is more in a longer wire As temperature increases the resistance increases since the electrons collide more often

6. Resistance A superconductor is a material that has almost zero resistance when it is cooled to low temperatures Superconductors are trying to reduce the resistance to zero The best superconductor has been cooled to 138K

7. Voltage In order for a charge to flow in a conducting wire, the wire must be connected in a complete loop that includes a source of electrical energy A flashlight will not work if there is no battery

8. Potential Difference Reminder potential energy is related to position Charges flow from a high to low potential energy Potential difference is the difference in electrical potential energy between two places in an electric field

9. Potential Difference Potential difference is measured in joules per coulomb or volts Potential difference is also called voltage

10. Voltage Sources Three common voltage sources are batteries, solar cells and generators A battery is a device that converts chemical energy to electrical energy In a 9-volt battery the voltage drop is about 9 volts

11. Ohm’s Law Named after German scientist Georg Ohm Ohm is the unit of resistance Ohm’s Law V = I x R or I = V/R Voltage (V) = current(I) x resistance (R) When the current is in amperes and the resistance is in ohms the voltage is in volts

12. Ohm’s Law What is the voltage if the resistance is 3 ohms and the current is 3 amps? V = I x R = 3 amps x 3 ohms = 9 volts Increasing the voltage increases the current Having the same voltage and increasing the resistance will decrease the current Multimeters measure current, voltage and resistance