Electronics tutorial: an intuitive idea of what voltage is


This time I am going to talk about voltage, trying to give the most intuitive intuitive interpretation possible: potential difference.

Actually, voltage is the potential difference between two points in an electric field per unit of charge. Does this sound familiar? Here is a clue: cinematic potential energy is the potential difference between two points of a gravitational field per unit of mass.

Plumbing circuit analogy

I was talking the other day with a friend about what would be the best way to intuitively understand what voltage is, and he told me that he really liked the water tower analogy.

Imagine we have two water towers, each has pipe leading to the ground and a valve to drain the water. Both towers contain exactly the same amount of water (assume that the water contained in the pipes is negligible) and the only difference between both towers is that A is higher than B.

Now, if you were to open any of the valves, out of which pipe would shoot water with more strength? I guess you said A, and you are right.

Because tower A is much higher than tower B, and considering that both valves are exactly at the same level, that is, ground level, each drop inside the deposit of A has more potential energy than they would have inside deposit B, therefore water comes out of A with more pressure.

In consequence, if we were to use the water to do some work, for example to drive a water mill, the water stream coming out of A would drive the mill much faster than B, and therefore, do more work.

Although we did not say it implicitly, the potential is a differential measurement. That means that it has to be measured between two points, in this case between the deposit and the valve. It is true that without knowing where the vales are you would still be able to correctly point out that the water in A has more potential energy that that in B, but you would not be able to tell me exactly how much more.

Electric voltage

The electric voltage is caused by the difference of energy that electrons have inside an electric field at a certain point with respect to the energy they would have on another point. You can also find a formal and an informal definition of voltage in a previous post.

In nature all atoms have the same amount of protons (positive charge) and electrons (negative charge), and coincidentally both have the same magnitude of charge (you could say that they are electrically the same size). So each proton and each electron cancel each other out.

But there exist processes in which electrons and protons can be separated, and in that scenario we have on one side an over-accumulation of electrons that repel each other, and on the other side ions (atoms with missing electrons) that try to attract new electrons to return to a neutral state. You could imagine electrons as if they were gas under high pressure inside a bottle that wanted to escape, so we can understand voltage as pressure.

So, higher voltage tries to move electrons with more force, and when we let them move we get a current which can be forced to pass through different devices to do some useful work, like lighting up a bulb.

Types of voltage


  • Positive: as in the previous analogy, water wants to escape the deposit. Now imagine that we continuously refill the same amount of water that escapes, in that case the deposit would have always the same amount of water and therefore the pressure at the bottom of the pipe be constant.
  • Negative: now imagine a deposit that tries to suck in water, or better yet, think about your vacuum cleaner. It tries to absorb, and for that it creates a negative potential.


An alternate voltage is a voltage that periodically (and usually at a fixed frequency) changes its polarity from positive to negative and then back from negative to positive. It does so in a continuous way, such as in a sinusoidal wave, as in the case of a wall plug.

Voltage signal

This is a voltage that varies in time and contains information, and is used for example as the electrical signal that your speakers use when playing music. Coincidentally, an analogy would be how air pressure vibrates around those speakers.

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