To understand how modern computers (I’ll ditch the ‘modern’ from now for the sake of brevity) work one must understand the basics of electricity and the operation of semiconductors.
Every electronic device around you is powered by a manipulation of the electrical force. Matter around us is made of atoms, which contain a positively charged proton, a negatively charged electron, and a neutrally charged neutron (hence the names). Two electrons, much like two protons, will repel each other (the force of repulsion grows exponentially as distance increases). A proton and an electron will attract each other. It might help to get an intuitive feeling the the electrical force if you imagine two electrons repelling each other the same way magnets do when they are brought together with their similar poles facing each other.
Looking at the big scale picture, we can make use of the repulsion and attraction that can be created by electrically charging objects positively or negatively. This can happen due to the fact that electrons can “flow” in all directions through material. For example:
The term “ground” being used in the above GIF means connecting the charged object with another object that can “absorb” or “give” electrons. The next image explains the idea of electron flow (or electric current) and the difference between an insulator and a conductor:
Electrons don’t fly through copper wires at the speed of light, they apply force on other electrons and nudge them. This forms a wave that propagates at speeds close to the speed of light. Each electron does move away from the negatively charged source, but in a sporadic fashion, causing it to advanced at a very slow pace (usually around a fraction of a millimeter per second in household electrical appliances).
The flow of electrons creates an electromagnetic effect (which is beyond the scope of this post) and also creates heat caused by all the electrons bouncing semi-sporadically around the conducting material. If you take a piece of conducting material thin enough, and cause a strong enough current of electrons, the material will light up in flames.
Interesting fact: The temperature of the conducting material affects its conducting abilities. Light bulbs work this way – burning is prevented by keeping the conducting filament in a vacuum tube, and the flow of electrons through the filament is balanced by the loss of conductivity due to the raising temperature of the filament.
The strength of flow is controlled by the amount of force driving it. If you take a metal sphere and over-saturate it with electrons, the repulsive force between the electrons will cause great electric tension inside the sphere. If the force of tension is strong enough, electrons could even rip through non-conductive materials coming into contact with the sphere. Another example of the effect of extreme electric tension is lightning – electrons ripping through the air, which is usually a good insulator.
From now on, we’ll use the following terms to describe the behavior of the electric force in objects around us:
Voltage is the difference in electric tension between two objects. Current is the flow of electrons through a material that connects these two objects, and the strength of the current depends on the Resistance of the connecting material. Lets take a look at the next examples for a more intuitive understanding of the connection between voltage, current and resistance:
- Connecting an electron saturated sphere (high electric tension) to the ground (low electric tension) through a thick copper wire (good conductor – low resistance) would cause a violent flow of electrons through the wire. In this situation, the voltage was high, resistance was low thus allowing the current to be high (strong).
- The same sphere is connected to the ground using a very thin metal wire. The wire will very quickly heat up due to the high voltage (strong electric force driving the electrons), further decreasing it’s conductive potential (increasing resistance) thus gradually restricting the current flow through it. In this situation, the voltage was high, but do to high resistance, the current was low (weak).
- Connecting an electron saturated sphere to another sphere which is a tiny bit less saturated with a thick copper wire would cause a flow of electrons through the wire. In this situation, the voltage was low, the resistance was low, and the current was low
Interesting fact: even though the earth’s surface is negatively charged, it will still absorb electrons from a negatively charged object, do to the density of charge, which will usually be higher in whatever negatively charged object you connect with the ground.
The mathematical connection between the voltage (V), current (I) and resistance (R) is simply described by Ohm’s law (circa 1830):
V = I * R
Given a voltage in a circuit containing at least two connected objects (with different electrical tensions), by having the number representing the resistance of the conductive material, one could calculate the number that represents the current that should flow through the circuit. Voltage is measured by Volts , Current by Amperes , and Resistance by Ohms.
These measurements and numbers are important. Over two centuries (starting from the 18th), through trial and error, mankind has domesticated electricity. Today every toddler knows that the socket in the wall has something to do with 220v (or 110v) of “electricity” and that you’ll get zapped if you stick your fingers in the terminals.
And it’s true, the voltage between the two terminals in the socket is 220v (or 110v). But what about the current? If you connect these two wires, the amount of current depends on the resistance of the connecting medium. If the resistance very low (thick copper wire), using Ohm’s law you’ll get a crazy high current (supplied by the transformer outside your house which is fed by the power-lines coming from a nearby power-station), meaning sparks will fly and something will probably burn.
In the next post, we’ll see how all of this applies to smaller circuits similar to the ones you’ll find in you computer.
Hope you found this post informative. Feel free to leave comments and replies.