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Current and Resistance
An introduction to Ohm’s Law

Recall: Potential Difference

Potential Difference Provided by the battery
AKA voltage measured in volts It is a “push” for the electrons in the wire that causes them to flow. The battery DOES NOT supply the electrons, they are already in the wire.

Current: The rate at which electrons flow through a conductor
𝐼= 𝑞 𝑡 Current: I measured in C/s (amp) The battery supplies the potential difference needed for the electrons to flow. THE BATTERY DOES NOT SUPPLY THE ELECTRONS THEMSELVES! Current only flows if there is a complete circuit!

Conservation of charge
Total current into a junction must equal the total current out. 3 Amps Magnitude and direction of current flow? 6 Amps 4 Amps In out 6 amps 4 amps 3 amps Total in: 9 amps Total out: 4 amps The unknown current is 5 amps out of the junction (to the right)

Simple Circuit Every Circuit must have
A source of potential difference (battery) A conducting material (wires) An electrical load (resistor/lightbulb)

Circuit Symbols Draw a circuit with a battery, a lamp and a switch using the symbols above

Resistance A resistor is any electrical device that you plug in.
It impedes the flow of electrons The resistance of an object is DIRECTLY related to temperature. The hotter the wires, the more resistance they have. The resistance of a wire depends on Its length The material its made of (resistivity) The cross-sectional area of the wire

Calculating Resistance
Resistance is measured in Ohms (Ω) Calculating Resistance

Circuits Measurements
Ammeter Voltmeter Measures current (in Amps) Wired IN SERIES with the resistor Has a very LOW resistance Measures potential difference (in Volts) Wired IN PARALLEL with the resistor Has a very HIGH resistance

Types of Circuits Series One complete loop Parallel Multiple paths

Ohm’s Law 𝑽=𝑰𝑹 Slope = Resistance V I Slope = 1/Resistance I V Resistance and current are INVERSES of each other. As one increases the other decreases! R I

Electrical Power When resistance is constant “ohmic”
“Follows ohm’s law” “constant temperature” When Potential Difference is constant P I P I

Electrical Power When resistance is constant “ohmic”
“Follows ohm’s law” “constant temperature” When current is constant P V P V

When Voltage is constant When current is constant
Electrical Power When Voltage is constant When current is constant P R P R

Electrical Energy (AKA work)
Measured in Joules

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