# Download U4D2 03.09 Notes

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Electric Current • Electric current is the movement of electric charge • Although it is the electrons that actually move, by convention, the direction that electric current flows is the direction that positive charge moves • Electric charge moves in response to a difference in electric potential between two locations • The charge moves (electric current flows) from the location with higher potential to the location with lower potential Electric Circuits • A pathway of charge movement is called an “electric circuit” • We are most familiar with electric current moving in a circuit made of wire, but that is not a requirement • An electric circuit must be “closed” for current to flow – the pathway must be continuous • If a gap exists in a circuit, we say that the circuit is “open” – electric current does not flow Ohm’s Law • The amount of current flowing in a circuit is • directly proportional to the potential difference • and inversely proportional to the resistance • The equation for this relationship is “I = V/R” • Current flow (I) is measured in “amperes” • Potential difference (V) is measured in “volts” • Resistance (R) is measured in “ohms” • This is “Ohm’s Law” – generally written V = I x R Voltage • The difference in electric potential that causes current flow is usually called the “voltage” • Voltage can come from a battery or a generator • We will look mostly at direct current (DC) circuits • Current flow will be in one direction • Voltage will be provided by a battery Resistance • The “resistance” in an electric circuit is all of the things that impede the flow of current • Sometimes these are devices that use the electrical energy such as lights or appliances • Sometimes these are devices, called resistors, that are used to limit the amount of current • Even the length, temperature, and diameter of the wire can affect the resistance in a circuit • long, hot, thin wires have greater resistance than short, cool, thick wires