Formula Mnemonics

I took a course in school (back in the late 1700's) called "Memory and Cognition" and it turned out to be very useful. One of the things I learned is that it is much easier to remember pictures than abstract concepts. As a result, I often devise pictorial representations of things I want to remember (like content for an examination). These pictures are often a bit weird, and some say I am too, but it sure seems to work for me. If it works for you, great. If not, you can join the crowd who think I'm weird.

So here are the pictures for basic ham formulas, with some explanations following:


Here are some comments to help you make sense of these diagrams:

-remember that E represents Electromotive force, which is another name for Voltage (see chart at top right of pictures for symbol definitions)

-The pie with what looks like a human ear in it is to remind you of the letters EIR PIE, which are the basis of the circular diagram just below the baked goods. These circles show you how to apply 2 basic formulas:

               OHM's Law:     E = I * R      voltage = current times resistance

   and the Power Law:     P = I * E      power = current times voltage

If you put your finger over one symbol in these circle diagrams, the remaining symbols show its formula according to the appropriate law. For example, if you cover the R for resistance in the first circle, what's left is E over I, so resistance = voltage over current. If you were to cover the E at the top of the first circle, you'd be left with I beside R. Symbols being adjacent implies multiplication in this case, and in formulas in general, so our finger work has shown that E = I * R, or voltage = current times resistance.

Below the circle diagrams are the formulas you derive from them, and a couple of extra ones you can get by combining them by substitution.

At the bottom of the left side of the picture are the 2 formulas for reactance. You only need to have a general knowledge of these.

There are two kinds of reactance:

     Inductive reactance, represented by XL             XL  =  2 * Pi * F * L
     Capacitive reactance, represented by XC          XC =           1          
                                                                                          2 * Pi * F * C

Note that L is the symbol for Inductance, and C is Capacitance, so these names actually make sense, perhaps unlike the memory aide I'm about to relate. Each of the formulas contains 2 * Pi * F, and I remember this by visualizing a guy who is about to get cream pies thrown at both sides of his face. Two Pies, against his Face:  2 Pi F. For the inductive case, you just multiply that by L, the inductance. For the capacitive case, you multiply by C, the capacitance, but then you have to put it below "sea (C)" level, and put it on the bottom of a fraction. Hey, it works for me.

You also need to understand what happens to reactance when frequency, inductance or capacitance vary. For XL , everything is multiplied together, so if either the frequency F or the inductance L get bigger, so does the inductive capacitance. If either gets smaller, so does  XL .

However, for  XC , the F and C are on the bottom of the fraction. So, if either gets bigger, the capacitive reactance gets smaller, and vice versa. (Yes, there's likely a question on the exam about that: B-005-010-001 to -003,  B-005-010-005 to -011 .)

The chart at the top right of the picture page is pretty self explanitory. One thing you have to remember is that all these formulas work on values that are simple standard units, for example, Ohms of resistance, and not milliOhms, microOhms, or KiloOhms. If you are given a value of 5 milliamps, you'll need to convert it to .005 amps before you can use it in a formula. Similarly, the result you get from applying a formula will be in standard units.

I don't think I'm up to explaining the CRISP AUNT MOANS chart at the moment, although it has a lot of useful information in it. I'll come back to this later, when I'm feeling more energetic.