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1
**Current and Resistance**

An introduction to Ohm’s Law

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**Recall: Potential Difference**

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**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.

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**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!

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**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)

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**Simple Circuit Every Circuit must have**

A source of potential difference (battery) A conducting material (wires) An electrical load (resistor/lightbulb)

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

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**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

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**Calculating Resistance**

Resistance is measured in Ohms (Ω) Calculating Resistance

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**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

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Types of Circuits Series One complete loop Parallel Multiple paths

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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

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**Electrical Power When resistance is constant “ohmic”**

“Follows ohm’s law” “constant temperature” When Potential Difference is constant P I P I

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**Electrical Power When resistance is constant “ohmic”**

“Follows ohm’s law” “constant temperature” When current is constant P V P V

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**When Voltage is constant When current is constant**

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

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**Electrical Energy (AKA work)**

Measured in Joules

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