# Formula Review

It has been quite prominently established that I hate math as much as you do. However, as you have also found, in order to have a CLEAR understanding of how electronic circuits and components work - a fairly decent grasp of the basic math functions is required. I absolutely promise you that the math is almost done. We've covered MOST of the math important to basic electronic components, and we will cover more - but I won't push it. That isn't to say that if you are using this as a supliment to classroom study - that your teacher won't give you a MAJOR math test right after you read this! That being said - I wouldn't want you to fail the test - so another review of the more important formulae may be in order:
In Review, the formula for finding Resistance, Voltage, and Current within a circuit (Ohm's Law) is:

or or

Much Akin to it is "Ohm's Watts Law" for finding POWER
P=IE

The Formula for finding the TOTAL RESISTANCE (or inductance in the case of a coil) in series is
R1+R2+R3... = RTotal

The Formula for finding the TOTAL CURRENT in series is

which we haven't covered because it is not a very important formula. Not so important because of the following formula which is also true:

I1=I2=I3... = ITotal

CURRENT NEVER CHANGES in a series circuit!!! In short - if you can measure the current ANYWHERE within the series circuit - you know the current in the whole circuit! (Very handy when checking Christmas lights)

The Formula for finding the TOTAL RESISTANCE in a parallel circuit is

The Formula for finding the TOTAL CURRENT in parallel is
I1+I2+I3... = ITotal

The formula for Time and Frequency is
F=1/T (or T=1/F)

The formula for Peak vs Effective voltage is:
EPeak=1.41xEEff or EEff=.707xEPeak
What is the formula for Inductive Reactance?

XL = 2πfL

RED? REALLY? Ok, perhaps I have stressed this point a bit too far, but then again, in electronics, and especially in radio electronics, you will see this formula again and again. Inductive reactance constitutes the resistance seen by an AC circuit when it runs into a coil. Sometimes, an inductor is called a CHOKE, because it chokes an alternating current flow. In power supplies, you may find a FILTER CHOKE, which opposes any ac frequencies, while allowing DC to pass through unharmed. Its purpose is to clean up the power supply voltages, so that no noise is seen on the power - just a clean DC source. There are both audio frequency chokes (AFC) and radio frequency chokes (RFC).

Another point, which I passed over previousely, is that there are several types of "RESISTANCE" found in AC electronics, some of which will be negligable, others you will find fascinating and extremely important to the study of electronics. I will try to cover in detail the important ones. I will also, (when I remember to) mention the lesser important ones, as I will at this time.

RELUCTANCE is a form of resistance which we have not discussed yet. The reason for not discussing it, is that in most electronic applications, you can pretend that it doesn't exist. Reluctance is actually the resistance, not to the flow of current, but to any MAGNETIC FIELD which cuts through any pre-existing magnetic field. To some small extent, this happens in all coils operating at AC, due to Self Inductance, or by way of Mutual Inductance. Mathematically speaking (oh no!) we say that it is equal to the MAGNETOMOTIVE FORCE / MAGNETIC FLUX, or that it is the reciprocal of PERMEANCE. Now, don't you feel safer? Isn't your life better, since you have learned that bit of trivia?
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