Learning The Basics

Voltage

Image Credit: WhoInventedFirst.com
Back in our school days, we all learned about sub-atomic particles and the atom. The atom is made of a central core, the nucleus. The nucleus contains a vast majority of the mass of the atom. The nucleus has a positive charge as it is made up of positively charge sub-atomic particles (protons) and particles with no charge (neutrons). For the purposes of this article, all you really need to know is that the nucleus is (usually) very stable and it's particles have no plans of going anywhere.

The electrons (negatively charged particles) are not so stable. They rotate around the nucleus and have the potential to move from their atom to another atom. This potential for electrons to move, between two different points, is voltage. This potential is measured in volts, surprise!

Current

Current is the actual flow of electrons.

Current is measured amperes, more commonly called Amps.

AC

AC stands for alternating current. This means that current, and therefore voltage, changes direction. A pictorial representation of AC is a sine wave.


Audio is AC voltage. As voltage moves in the positive direction, or upwards in your pictorial representation, your speaker driver moves outwards ( this is called rarefaction).
As voltage moves in the negative direction, or downwards in your pictorial representation, your speaker driver moves inwards ( this is called compression).



Your home also runs on AC Voltage. One of the main reasons for this is because AC voltage can be stepped up or down very easily with the use of a transformer. For example, the "power line" carrying electricity to your home runs on a much higher voltage; a transformer is then used to step this down to the standard 120V.


DC

DC stands for direct current. Batteries, power supplies, and a significant amount of electronic circuitry operates in the DC realm. This is true even inside your audio gear; for example, you have circuits and chip-sets that are designed for certain tasks like DSP (digital signal processing). These are all DC circuits.

When looking at DC on x, y graph it looks like a straight line.

Impedance/Resistance

Resistance is a bit self-describing, and is simply how resistant something (component or material) is to the flow of electrons.

Simply put, impedance is resistance in an AC circuit. Realistically, it is more complicated than basic resistance in a DC circuit ( mentioned above and also known as ohmic resistance) as it is also comprised of reactance (see below). For most beginner applications, you will consider these interchangeable - just keep in mind that when impedance is mentioned, you are discussing an AC circuit.

Both are measured in Ohms.

Ohm's Law


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Ohm's law states that:

Voltage = Current X Resistance . This is denoted as V=IR . V=Voltage; I=Current; R=Resistance.

Using algebra, you can rearrange the equation to calculate for current or resistance. 

For example:

Current = Voltage / Resistance or I= V/R.
Resistance = Voltage/ Current or R=V/I





Continuity

This means that something is directly connected electrically. For example, when checking a fuse you would use your multi-meter to see if both ends share continuity; if so the fuse is good. If not, the fuse is blown. This can also be used to test if a component (i.e. resistor, diode, etc.) is shorted.

Reactance

Reactance is also resistance to the flow of electrons in an AC circuit specifically due to its alternating nature. Unlike Ohmic resistance, reactance is not based on a materials conductivity. A magnetic field or a stored charge resist the change in the flow of electrons. Reactance is the resistance to the flow of electrons due to stored charges or magnetic fields.

Reactance is also measured in Ohms.

Capacitance 

Capacitance is the ability to store an electrical charge. The higher the capacitance, the greater the ability to store a charge.

Capacitance is measured in Farads.