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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
• 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
• 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