Electricity
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Electricity . Part 2: Electric Current. Electric current is the amount of charge moving past a point. Maxwell Demon counting the charges passing a given point. Definition of current. I = current Q = amount of charge that passes point. t = time for charge to pass by. Units of Current.

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Electricity

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Electricity

Electricity

Part 2: Electric Current


Electric current is the amount of charge moving past a point

Electric current is the amount of charge moving past a point

Maxwell Demon counting the charges passing a given point


Definition of current

Definition of current

  • I = current

  • Q = amount of charge that passes point.

  • t = time for charge to pass by.


Units of current

Units of Current

1 Ampere (Amp) = 1 Coulomb/second


Electric currents only flow in wires

Electric currents only flow in wires.

  • True

  • False


Examples of currents

Examples of Currents

Solar wind interacting with the earths magnetic field


Electricity

1) Coronal Mass Ejection

2) Aurora from space

3) Aurora from ground

CME animation

Aurora from space

Aurora effects


3 electron beams in a color tv

3 electron beams in a color TV


Tokamak fusion experiments jet discharge

Tokamak Fusion ExperimentsJET discharge


We usually think of currents in wires opening switch

We usually think of currents in wiresOpening switch


Simple circuit

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.


Ohm s law v ir

Ohm’s LawV=IR

  • V= Voltage of the Battery.

  • I=current in circuit.

  • R=Resistance in the bulb/resistor. (Depends on materials and geometry.)


Units of resistance

Units of Resistance

  • R=V/I (volts/amps)

  • By definition, 1Ohm = 1 volt/amp,

    or

    1=1V/A.


Electricity

Log Ride Analogy


Water circuit analogy

Water circuit analogy


Example problem

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.


Power in a circuit

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.)


Electricity

  • 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)


Electricity

  • The power supplied by the battery must be dissipated in the resistor.

  • We also know the V=IR.

  • Power dissipated in resistor


Which type of light bulb has a larger resistance a 100w bulb or a 60w bulb

Which type of light bulb has a larger resistance, a 100W bulb or a 60W bulb?

  • The 100 W bulb

  • The 60 W bulb

  • They will have the same resistance

  • None of the above


Example calculation

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.


Electricity

  • Redo the calculations for a 60 W bulb


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