For historical reasons there is a lot of confusion regarding two of the most fundamental aspects of electronics.
Electrons are defined as having
a ‘negative’ charge.
The current flowing in a circuit
goes the ‘wrong way’.
Both of these problems came from the way electronics developed out of much earlier studies of electrostatics. Electrostatic charges were originally generated by rubbing things together — for example rubbing a glass rod with a piece of silk. The rubbing ‘scrapes off’ some electrons from one object and collects them on the other. As a result, both the objects pick up equal and opposite charges.
The early ‘natural philosophers’ (that's what scientists were called then — things change, eh?) discovered the opposing natures of these charges and called one type negative and the other positive. Later on it turned out that the objects which were said to have gained a negative charge had picked up extra electrons. Hence we had to define the electron's charge as being negative to make things come out right!
The early work on electric current was based on building batteries. This was done in various ways. For example, the Italian scientist Volta (the ‘Volt’ is named after him) built stacks of alternating materials to make multi-cell batteries which gave quite high voltages. Using pairs of wires he could connect them to frogs legs (what else?) and observed that they gave a ‘kick’. This was similar to the effect produced by discharging an electrostatic charge, so it became clear early on that there was some kind of link between this kind of electricity and electrostatic charges.
However, it was also clear that a battery could produce a continuous effect. For example, putting the wires into a glass of water produced steady streams of bubbles. And if you used a big battery to give someone a shock and make them jump you could keep on doing it (if they didn't thump you!) without having to keep on renewing the charge. From experiments like this came the idea of a steady flow of charge around a circuit whenever you made a closed loop.
Alas, when the early scientists defined ‘which way around’ the current went they managed to get it wrong. They naturally defined current as always flowing from positive to negative. Later on, when this idea was brought together with the discovery of the electron it became clear that electrons, being negative, actually went the other way around the loop.
All of this simply demonstrates one of the basic laws of thermodynamics: that you can't win!...
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Content and pages maintained by: Jim Lesurf (jcgl@st-and.ac.uk)