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Electricity Part 2: Electric Current

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Electric current is the amount of charge moving past a point Maxwell Demon counting the charges passing a given point

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Definition of current I = current Q = amount of charge that passes point. t = time for charge to pass by.

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Units of Current 1 Ampere (Amp) = 1 Coulomb/second

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Electric currents only flow in wires. 1.True 2.False

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Examples of Currents Solar wind interacting with the earths magnetic field

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1) Coronal Mass Ejection 2) Aurora from space 3) Aurora from ground CME animation Aurora from space Aurora effects

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3 electron beams in a color TV

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Tokamak Fusion Experiments JET discharge JET discharge JET discharge

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We usually think of currents in wires Opening switch Opening switch Opening switch

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Simple circuit When a charged particle passes through the battery, it gains energy. When the particle passes through the light bulb it gives up the energy as heat.

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Ohm’s Law V=IR V= Voltage of the Battery. I=current in circuit. R=Resistance in the bulb/resistor. (Depends on materials and geometry.)

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Units of Resistance R=V/I (volts/amps) By definition, 1Ohm = 1 volt/amp, or 1 =1V/A.

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Log Ride Analogy

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Water circuit analogy

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Example problem How many amps of current would flow in a light bulb that has a resistance of 60 if it is connected to a 12 V battery.

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Power in a circuit When Charge Q passes through the battery it gains an amount of energy E=( Q)V (This is the amount of work the battery does on the charge.)

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If the charge takes an amount of time t to pass through the battery, the battery supplies a power of (does work at a rate of)

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The power supplied by the battery must be dissipated in the resistor. We also know the V=IR. Power dissipated in resistor

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Which type of light bulb has a larger resistance, a 100W bulb or a 60W bulb? 1.The 100 W bulb 2.The 60 W bulb 3.They will have the same resistance 4.None of the above

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Example Calculation What is the resistance and how much current flows through a 100 W bulb? Note: The wattage on a bulb is its power output and assumes that you will use it in the US where the voltage in 110 V.

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Redo the calculations for a 60 W bulb

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