Monday, January 17, 2011

Lesson 22: General Class Exam Course G5C

Here is lesson 22 and some math for hams.  This lesson mostly covers how to calculate total resistance, capacitance, and inductance in a circuit.  The formulas you need to know are below.  You may want a calculator for this lesson.

First, a definition you will need to memorize:

Magnetizing current is the current in the primary winding when no load is attached to the secondary winding.

The formulas:

To calculate total resistance for resistors in parallel:
Total R = 1/[1/R1 + 1/R2 + 1/R3 + 1/Rn...]

To calculate total resistance for resistors in series:
Total R = R1 + R2 + R3 + Rn...

To calculate total inductance for inductors in parallel:
Total Inductance = 1/[1/I1+ 1/I2 + 1/I3 +1/In...]

To calculate total inductance in for inductors in series:
Total Inductance = I1 + I2 + I3 +In...

Total inductance and resistance in a circuit are calculated in the same manner for components in series and in parallel.  Total capacitance is calculate in the opposite manner.

To calculate total capacitance for capacitors in parallel:
Total Capacitance = C1 + C2 + C3 + Cn...

To calculate total capacitance for capacitors in series:
Total Capacitance = 1/[1/C1 + 1/C2 + 1/C3 + 1/Cn...]

To find the voltage across the secondary winding in a transformer divide the volts AC connected to the primary winding by the ratio of primary turns to secondary turns.

VAC/(Primary turns/Secondary turns)

The turns ratio for of a transformer is the square root of the impedance ratio.  If you know the impedance you need to match:
(Square Root of Impedance 1/Impedance 2) : 1

Good luck.  As you will probably notice, I'm not a math teacher!  If you have any suggestions, questions, or comments, please feel free to leave them in the comments box.

73,
Andy
KE4GKP

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