InductorInductor

Physical CoilPhysical Coil A circuit component A circuit component

designed for inductance is designed for inductance is an an inductorinductor..• Symbol suggests coiled wireSymbol suggests coiled wire

Ideal inductors act like wires Ideal inductors act like wires unless the current changes.unless the current changes.• Emf based on LEmf based on L

Real inductors have some Real inductors have some resistance.resistance.• Resistivity of length of wireResistivity of length of wire

RL CircuitRL Circuit An inductor resists changes in An inductor resists changes in

current.current.• Creates emfCreates emf

A switch can be used to A switch can be used to complete a circuit with a complete a circuit with a resistor.resistor.• One-loop Kirchhoff’s lawOne-loop Kirchhoff’s law

• Treat as additional emf sourceTreat as additional emf source

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Inductive Time ConstantInductive Time Constant

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The voltage across an inductor The voltage across an inductor falls with time.falls with time.• Change in current decreasesChange in current decreases

• Never reaches zeroNever reaches zero

• Overall current increasesOverall current increases

The period of time for a The period of time for a decrease by a factor of decrease by a factor of ee is the is the time constant time constant ..

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Exponential Decay Exponential Decay The emf of an inductor can be The emf of an inductor can be

represented by an exponential represented by an exponential curve.curve.• Depends on battery voltageDepends on battery voltage

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Inductor CurrentInductor Current Inductor and resistor voltages Inductor and resistor voltages

sum to battery voltage.sum to battery voltage.• Kirchhoff’s voltage lawKirchhoff’s voltage law

Circuit current can be Circuit current can be determined from Ohm’s lawdetermined from Ohm’s law

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DisconnectionDisconnection Opening a switch with current Opening a switch with current

flowing is a change in current.flowing is a change in current.

The inductor will create an emf The inductor will create an emf to resist the change.to resist the change.

For a large current the emf can For a large current the emf can create a spark.create a spark.

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Safe DischargeSafe Discharge A pair of opposite switches can A pair of opposite switches can

provide a safe path for current provide a safe path for current in an inductor.in an inductor.• A and B always in opposite A and B always in opposite

positionposition

When switch A is closed the When switch A is closed the battery powers the circuit.battery powers the circuit.

When switch B is closed the When switch B is closed the inductor current flows through inductor current flows through the switch and resistor.the switch and resistor.

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