Ohm's Law

This is a very important rule to understand, it should help you understand circuits better than before. This article will give you basic definitions of Resistance, Current and Voltage. Then you will learn ohm's law and a way to use it.

Resistance (R)

Resistance is a measure of how hard it is for electrons to get through a substance. The units of resistance are ohms. Wires have very close to 0 resistance. Resistors have a specific amount of resistance, useful for building circuit. Resistance is related to current and voltage through Ohm's Law.

Current (I)

Current is a measure of how many electrons per second go through a certain point. This is measured in Amps. Usually in tube amplifiers you will get a small currents, in the range of mA, and high voltages, around 300V maximum.

Voltage (V or E, we'll use V)

Voltage is the most recognized and usually least understood of all these terms. Voltage can be thought of as a force. With a certain amount of voltage one can power a vacuum tube or any other device you think of. Without voltage electrons have nothing to push them through.

Voltage is also a relative measurement. This means that when you measure voltage between ground and a wire the voltage measured is the difference between the two. To make things simpler everyone considers ground as 0V and they usually measure voltages in reference to the ground.

Ohm's Law

V=IR (Voltage=Current*Resistance

If you have trouble understanding an algebraic equation that is not a problem since I have listed out some things you are able to calculate using this equation.

To get an answer from this equation you have to know two out of three of the variables. I have listed one ways to use this equation below.

Measuring the Current through a Resistor

Set your multimeter to measure volts, if you don't know please read the Multimeter Tutorial
Put the red lead on one side of the resistor and the black lead on the other side of the resistor. The only thing between the leads should be the resistor
Measure the voltage, lets say you measured 2V
Read the resistor value. If you don't know how then go to Reading Resistor Values.
I=V/R, so current=voltage/resistance. When doing this math, if you have prefixes on your units make sure you convert you unit to a normal unit without a prefix (22k Ohms, use 22,000 in your calculator).
If R=100 then I=2/100=.2amps

If you have any comments or suggestions please let me know. Thank You.