Inductor Physical Coil A circuit component designed for

Inductor

Physical Coil ] A circuit component designed for inductance is an inductor. • Symbol suggests coiled wire ] Ideal inductors act like wires unless the current changes. • Emf based on L ] Real inductors have some resistance. • Resistivity of length of wire

RL Circuit ] An inductor resists changes in L I(t) current. • Creates emf V R ] A switch can be used to complete a circuit with a resistor. • One-loop Kirchhoff’s law • Treat as additional emf source

Inductive Time Constant ] The voltage across an inductor falls with time. • • • Change in current decreases Never reaches zero Overall current increases ] The period of time for a decrease by a factor of e is the time constant t.

Exponential Decay ] The emf of an inductor can be represented by an exponential curve. • Depends on battery voltage

Inductor Current ] Inductor and resistor voltages sum to battery voltage. • Kirchhoff’s voltage law ] Circuit current can be determined from Ohm’s law

Disconnection ] Opening a switch with current L I(t) V flowing is a change in current. R ] The inductor will create an emf to resist the change. ] For a large current the emf can create a spark.

Safe Discharge ] A pair of opposite switches can provide a safe path for current in an inductor. • A and B always in opposite position ] When switch A is closed the battery powers the circuit. ] When switch B is closed the inductor current flows through the switch and resistor. SA I(t) V SB L R