Circuit basics: Voltage

Almost everyone knows voltage as something that's coming from the socket in the wall. But what does it do exactly?

Voltage is the difference in electronical potential between two points. For example a battery has two point, the + and the - poles.  You can imagine electronical potential as a large water tank under pressure. The amount of 'pressure' is measured in volts. The + pole is at full pressure (1.5V for example) the - pole is at zero pressure. Upon connecting the two tanks, water will flow between the tanks which is the current. When the pressure in tank + and tank - is equal, water will no longer flow between them.

Within our circuits the battery (or power supply) is delivering the voltage. In the following circuit a battery is connected to a voltmeter: 

1 x Multimeter
1 x 3V power supply

The volt meter should read the voltage between te + and - pole of the battery. Let's see how this works out in real situation:

As you can see, the volt meter read 2.9 volts. This is because the battery is not delivering the promised 3V and the volt meter has a tolerance of about 1-2%. In practice this doesn't really matter, as most electronic component have a tolerance too.

Next we'll see what happens when components are put in series:


1 x Multimeter
1 x 3V power supply
1 x 150 Ohm resistor (brown green brown gold)
1 x Red LED

The resistor and LED are put in series. Also three volt meters are shown. You will notice that the sum of the two voltmeters put in series is equal to the volt meter on the right. This means that sum of the voltage over each component put in series is equal to the voltage of the power source. So how is it possible that the LED has a different voltage than the resistor? That's because of the resistance. I will blog about it later.

Finally a circuit where two LED's are put in parallel:

1 x Multimeter
1 x 3V power supply
1 x 150 Ohm resistor (brown green brown gold)
2 x Red LED

As you can see, the voltage over both LEDs is equal. This means that components in parallel have the same voltage.