Basic Electricity

Here's a post that's mostly for my own studies, but I hope others will find it useful.

Current is the flow of electrons. It is represented by the letter I. Current is measured in Amperes, which is represented by the unit A. Current is measured with an ammeter.

Voltage is the electro-motive force of electricity. It is represented by the letter E. Voltage is measured in Volts, which is represented by the unit V. Voltage is measured with a voltmeter. Voltage is measured from a reference voltage, which is usually ground. Voltage also has a polarity; positive polarity attracts electrons, while negative polarity repels them.

Resistance is the impedance of current. It is represented by the letter R. Resistance is measured in Ohms, which is represented by the unit Ω. Resistance is measured with an ohmmeter.

Ohm's Law defines the relationship among current (I), voltage (E), and resistance (R).

R = E / I

You can solve the equation for the others with some quick math.

E = R * I
I = E / R

Power is the product of voltage (E) and current (I). It is represented by the letter P. Power is measured in Watts, which is represented by the unit W. Power is not measured directly and must be calculated.

P = E * I

Again with some quick math.

E = P / I
I = P / E

Using the equations from Ohm's Law, we can substitute values for voltage (E) and current (I) in to the Power equation. Since E = R * I, we can say that P = (R * I) * I or RI^2. Also, since I = E / R, P = E * ( E / R), or E^2/R.

P = E^2 / R
P = R * I^2