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Inductance

In the figure below, when the switch is closed, the battery produces an electric current, which induces a magnetic effect or field.   The red line in the figure depicts the magnetic field.  If one were to take a magnetic compass, which faces North-South in the direction of the earth’s magnetic field, and place it next to a wire that is carrying a current, the compass needle deflects away from its North-South orientation.

 

Likewise, if one would replace the compass with another coil, the second coil would respond to the magnetic field created between the 2 coils which in turn would cause a voltage at the terminals of the second coil. See above sketch:
This above phenomenon are examples of Inductance. More specifically, the voltage at the second coil in the bottom figure is created by Mutual Inductance.

Inductance It is measured in henrys: symbol, L

Typical values of Inductance are either in millihenrys mH (one thousand of a Henry) or microhenrys uH (one thousand of a Henry).

Inductors in Series –

In the following figure, two Inductors are in series.  When two inductors are in series the total inductance exclusive of  Mutal Inductance = L1+ L2  measured in henrys.  Now if  the coils are close enough physically, the magnetic fields that the coils generate will interact causing a Mutual Inductance.

This must be accounted for by stating that the total inductance = (L1+M) + (L2 + M) or (L1-M) + (L2 – M) which can be rewritten as Total Inductance = L1 +L2  +/- 2M where M is the Mutual Inductance which depends on whether or not the coils magnetic fields aid each other (+)  or oppose each other (-). 


Inductors in Parallel –

In the following figure two Inductors are in parallel.  When two inductors are in parallel the total inductance exclusive of  Mutal Inductance = 1/L1+ 1/L2  measured in henrys. 

Now if  the coils are close enough physically, the magnetic fields that the coils generate will interact causing a Mutual Inductance (M). This must be accounted for by stating that the total inductance = 1/(L1+M) + 1/(L2 + M)

or 1/(L1-M) + 1/(L2 – M)  where the Mutual Inductance (M)  depends on whether or not the coils magnetic fields aid each other (+)  or oppose each other (-). 

Typical values of Inductance are either in millihenrys mH (one thousand of a Henry) or microhenrys uH (one thousand of a Henry).

Model Train Applications

(1) Manufacture of relay coils which can be used to throw turnouts or switches to control train direction, or select electrical signal paths. Basically the inductor surrounds a magnet. As the coil is energized with a voltage, the magnetic field will cause the magnet to move, thus causing electrical contacts to move. It is a way from converting electrical energy to magnetic and then to mechanical motion.

(2) The inductance caused by long wire runs that cross higher voltage runs can play havoc with a train layout. In other words a 115 vac wire run can cause interference if  it  is within a couple of inches from a digital low level set of pulses.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

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