1. Chapter 6 Inductance

2. 23/15/2016 N S S v change Review example Determine the direction of current in the loop for bar magnet moving down. Initial flux Final flux By Lenz’s law, the induced field is this

3. Self Inductance 3 A self-induced emf is always proportional to the time rate of change of the current. For any coil, we find that where L is a proportionality constant—called the inductance Combining this expression with Faraday’s law, We can also write

4. 43/15/2016 Inductor in a Circuit Inductance can be interpreted as a measure of opposition to the rate of change in the current Remember resistance R is a measure of opposition to the current Remember resistance R is a measure of opposition to the current As a circuit is completed, the current begins to increase, but the inductor produces an emf that opposes the increasing current Therefore, the current doesn’t change from 0 to its maximum instantaneously Therefore, the current doesn’t change from 0 to its maximum instantaneously Maximum current: Maximum current:

5. 53/15/2016 20.9 Energy stored in a magnetic field The battery in any circuit that contains a coil has to do work to produce a current Similar to the capacitor, any coil (or inductor) would store potential energy Summary of the properties of circuit elements. ResistorCapacitorInductor units ohm,  = V / A farad, F = C / Vhenry, H = V s / A symbolRCL relationV = I RQ = C V emf = -L (  I /  t) power dissipated P = I V = I² R = V² / R 00 energy stored0PE C = C V² / 2PE L = L I² / 2

6. 63/15/2016 Example: stored energy A 24V battery is connected in series with a resistor and an inductor, where R = 8.0  and L = 4.0H. Find the energy stored in the inductor when the current reaches its maximum value.

7. 73/15/2016 A 24V battery is connected in series with a resistor and an inductor, where R = 8.0  and L = 4.0H. Find the energy stored in the inductor when the current reaches its maximum value. Given: V = 24 V R = 8.0  L = 4.0 H Find: PE L =? Recall that the energy stored in th inductor is The only thing that is unknown in the equation above is current. The maximum value for the current is Inserting this into the above expression for the energy gives