1. Self - Inductance
Faraday postulated that a magnetic field consists of lines of force surrounding the current-carrying conductor.
Think of these lines as elastic bands that close on themselves.
As the current increases and decreases, the bands expand and collapse about the conductor.
ECE 201 Circuit Theory I

2. Self – Inductance continued
Compress for decreasing magnetic field (due to decreasing current).
Faraday’s Law : the voltage induced into the conductor is proportional to the number of lines that cut the conductor.
Expand for increasing magnetic field (due to increasing current).
ECE 201 Circuit Theory I

3. Faraday’s Law
λ is called the “flux linkage” and is measured in weber-turns
ECE 201 Circuit Theory I

4. Magnetic field linking an N-turn coil
ECE 201 Circuit Theory I

5. Permeance, P
Permeance describes the magnetic properties of the space occupied by the flux.
Units are webers/ampere-turn.
ECE 201 Circuit Theory I

6. ECE 201 Circuit Theory I

7. Voltage Polarity When i increases, di/dt is + and v is +.
Energy produces the magnetic field
ECE 201 Circuit Theory I

8. Voltage Polarity When i decreases, di/dt is - and v is -. i is still +
Magnetic field collapses - +
ECE 201 Circuit Theory I