1.3 Voltage

Definition of voltage

Voltage is the amount of energy per unit of charge. There it is, the definition of voltage. In formula form:


A definition that perhaps does not really help to get an intuitive understanding of the meaning of voltage, also because energy is a rather abstract quantity. Energy is what you need to push electrons through a wire, a light bulb, a heating element (e.g. in your toaster), or any other electric or electronic component. It can be compared with the energy in the fuel for your car. Without fuel, the car can not ride. The fuel delivers the energy to accelerate the car, and to maintain a constant speed while opposing the forces caused by friction, air (aerodynamics), and rolling resistance. If you would translate the concept of voltage to car fuel, you could say that your fuel’s voltage is the amount of energy it contains for each fuel molecule. Note however that this concept is not used in practice.

An indispensable component in any electric or electronic circuit is some source of energy. Very often this is a voltage source, like a battery (see later section). This source will give energy to the electrons that enables them to move through the circuit. In general, a source having a higher voltage makes the electrons go faster (because they have more energy), so leading to higher currents.

For the moment, we will not discuss the concept of voltage in detail. A deeper understanding will be gained if it is combined with the concept of current, and how these to relate to each other. This relationship will differ for each component. Indeed, it will turn out that components like resistors, diodes, capacitors and voltage sources each have a different voltage-current relationship.

Some notes on symbols and units.

In this e-book, the symbol V will be used for voltage. This is not according to some official standards, but since many electronic engineers stick to this symbol, it will be adopted here as well. The unit of voltage is the volt, abbreviated by the symbol ‘V’. Indeed, this might give rise to some confusion, since the same symbol is used for the physical quantity and the unit, but from the context it will always be possible to derive which of both (the quantity or the unit) is referred to. As an example, if the voltage across a certain resistor is 2 volt, it will be denoted as:

VR = 2 V

From the definition, it can be derived what 1 V means. 1 V corresponds to 1 joule per coulomb, or 1 V = 1 J/C. However, it is difficult to grasp the meaning of this without a concrete example. This will be clarified in later sections.

Things to remember

  1. The symbol for voltage is V.
  2. The unit of voltage is the volt, abbreviated with V.
  3. The voltage corresponds to the amount of energy per unit of charge.
  4. A higher voltage means that the electrons have more energy.

Go to 1.4 The resistor

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