Loading phys212..

30.8-30.10

Inductance

Faraday's law applied to a solenoid shows that you will induce an EMF when the B field changes (see problem solving video on next page).

So imagine that you have a circuit element which is a wound up piece of wire (like in a solenoid). In such circuit elements, the B field changes when the current changes. By Faraday's law, an EMF will be induced to oppose the change in current. The end result, is that if we were to place a solenoid inside a circuit there would be a negative drop in voltage on the solenoid when the current changes.

\Delta V_L = -L \frac{dI}{dt}

where L is the inductance, in units called the Henry (H). Just like capacitance, inductance depends of the physical way you constructed the inductor. For example, the inductance could depend on the shape of the solenoid, its length, number of turns etc.

An ideal inductor is ultimately just a wire which, ideally, would have zero resistance. So in a steady-state circuit (that means after a long time when nothing is changing), the current is constant and the inductor behaves like a wire. A wire can be considered a zero resistance resistor. So an inductor can be used to "short" parts of a circuit. In real life, in order to get large inductance with a solenoid, one must have very very long wires and the resistance often becomes non-negligible.

Reading Guide

Look at the review material about oscillator and RC circuit. The LC circuit behaves like a simple harmonic oscillator while the LR circuit is more similar to the RC (exponential decay of current).

Make sure to carefully work out example 30.12 to 30.16. The challenge example 30.17 is not needed.

Please use a modern browser to view our website correctly. Update my browser now