This is part two in our series on basic electronics. Part one is Electron, Proton, Neutron.









An electrical circuit allows electrons to flow from one side of the circuit to the other. The two ends of the circuit have a difference in electrical charge. One side is more positively charged then the other. Electrons are attracted to the positive side and move through the circuit. The electrons move from the negative side of the circuit to the positive but we say the electrical current flows from the positive to the negative. It is the attractive force emanating from the positive side of the circuit that we call the current.







This diagram shows a simple LED driver circuit. When the battery is connected the positive end of the battery pulls electrons from the negative end of the battery and through the circuit. This circuit has three basic properties we can use for measurement and analysis. They are voltage, current, and resistance.

Voltage
The amount of difference in electrical charge between the two sides of the circuit is called the voltage. Higher voltage power sources will have more attractive force. Voltage can be considered electrical pressure pulling electrons through a circuit.

Current
While the voltage moves the electrons through the circuit they cannot all go at once. The rate at which the electrons move through the circuit is called the current. We measure the current in amperes. One amp is about 6.241×10¹⁸ electrons passing through a point in a circuit in one second.

note: 6.241x1018 is an easier way to write a big number. It stands for the number 6,241,000,000,000,000,000.

Resistance
Because of the electrical pressure the electrons would like to move at a very high current but some materials conduct electricity better then others. Materials that have a high resistance conduct electricity less well. Resistance limits the flow of electrons between the two ends of the circuit. We measure resistance in units called ohms (Ω). One ohm is defined as the amount of resistance you have in a conductor when applying one volt of electrical pressure creates one amp of current.

Ohm’s law
Voltage, current, and resistance have a mathematical relationship which we can use to calculate the properties of the circuit. Ohm’s law states that the current is directly proportional to the voltage and inversely proportional to the resistance. The formula looks like:

The current equals the voltage divided by the resistance.

It can also be written:

The voltage equals the current multiplied by the resistance.

Or, you can write it like this:

The resistance equals the voltage divided by the current.

They are all the same. Using these equations, if you know any two of the values you can calculate the third.

Looking again at our LED driver circuit let’s try to figure out the current through the circuit. If we use a 3 volt battery to power the circuit and a 220 Ohm resistor then what should the current through the circuit be?

So lets’ recap. Voltage is like electrical pressure. It is the amount of difference in charge between the two sides of the circuit. Current is how quickly the charge moves from one side to another. Resistance holds back the electrical pressure, impeding the current. Higher voltage creates high current. High resistance causes lower current.

Stay tuned for our next article.

Ariel Churi || In: Learn | | permilink