1. Inductor

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

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

4. Inductive Time Constant  The voltage across an inductor 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 decrease by a factor of e is the time constant .

5. Exponential Decay  The emf of an inductor can be represented by an exponential curve. Depends on battery voltageDepends on battery voltage

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

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

8. Safe Discharge  A pair of opposite switches can provide a safe path for current in an inductor. A and B always in opposite positionA 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. R I(t)I(t) V L SASA SBSB