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Ch 32 Inductance
32.1 SelfInductance Consider this circuit
When the switch is closed, the current increases, causing a changing flux into the loop. A "back emf" is induced, opposing this change in flux and rise in current. The circuit induces a current in itself. This is self inductance.
where "L" is theinductance of the circuit (or circuit element). Circuit elements designed to provide a specific amount of inductance are usually coils of wire.
Units:
Example: The inductance of a (ideal) solenoid
Example: Going back to the MRI macine we considered a chapter ago, it had 50,000 turns, was 0.800 m. If it has a radius of 45.0 cm, what the inductance of this coil. (Assume it's an ideal solenoid.)
Example: Take an RL circuit hooked up to a 12.0V battery
with R = 100. Ω and L = 250. mH. Sketch I(t) and find the
current at t= 4.00 ms.
32.3 Energy in a Magnetic Field In effect an inductor "stores" current flow or it "stores" magnetic field energy
This is the energy stored in an inductor carrying a current "I." We can also think of the energy density in the magnetic field:
For a solenoid:
This is actually applicable to any B field; it's the energy stored in the field itself.
Example: Consider 2 "nested" solenoids. Find their mutual
inductance if the first coil has 1000 turns, the second has
250 turns, their area is 0.000700 m² and they are 2.50 cm
HW Ch 32 pp 10251027:
P 1, 5, 10a, 15, 27, 30, 39, 43
