5. Electrical voltage

The electrical voltage of a generator, also called electric voltage, is the energy with which the generator drives electrons in an electrical circuit.

All electrical circuits need at least one generator that drives electrons through the circuit. The generator acts as a water pump with electrons, forcing them to move through the electrical circuit.

Volts

The electrical voltage is measured in volts, shortened with [V]. In the following table the typical tensions of several common generators appear in our surrounding:

Generator Tension [V]
AA type alkaline battery. 1.5 volts
Lithium button stack. 3 volts
Battery of a smartphone. 3.6 volts
USB connector 5 volts
Laptop loader. 20 volts
Wall plug. 230 volts
Medium voltage transport line. 22,000 volts

Earth voltage

The voltage of the Earth (the terrain on which we are) is considered to be worth zero volts and is the absolute reference of any electrical circuit. A copper bar of one meter in length is normally numbered on the ground, to which a cable with yellow and green colors is connected.

_images/electric-toma-tierra.jpg

Grounding with their yellow-green cable.

Ali K, CC BY-SA 3.0 Unported, via Wikimedia Commons.

From earth voltage, tensions can be both positive and negative. In the circuits the earth symbol is usually drawn to indicate what we consider zero voltage.

In the following simulator we can observe several series generators who add their tensions. The green color indicates positive tensions and the red color indicates negative tensions. The earth symbol indicates absolute zero tension.

Voltmeter

The voltmeter is a device that measures the voltage difference between two points of a circuit. Voltmeters are always connected in parallel with the elements to be measured.

To simulate a voltmeter we must choose it from the menu Draw... Meters and Labels... Add Voltmeter.

In the following simulation, add the necessary voltmeters to measure the tension of the two batteries together (V1 plus V2), the tension of the L1 lamp and the tension of the L2 lamp.

Exercises

  1. What is electrical voltage or voltage?
  2. Why do all electrical circuits need at least one electric generator?
  3. What voltage in volts have typical batteries and batteries?
  4. What is earth tension?
  5. What is a voltmeter? How should it be connected to measure tension?