Article by Massimo Banzi www.potemkin.org/cms/Pid/BasicsOfElectricity
If you have ever done any plumbing at home, electronics wonâ€™t be a problem for you to understand. Jokes aside, in order to understand how electricity and electric circuits work the best way is to build yourself a mental model called the â€œwater analogyâ€. Letâ€™s take a simple device like a portable fan, if you take it apart you will see that it contains a small battery a couple of wires going to an electric motor and one of the wires is interrupted by a switch. Now makes sure you have a new battery fitted in the device and activate the switch; the motor will start to spin providing the necessary refreshment. How does this work? Well imagine that the battery is a water pump and the switch is a tap while the motor is one of those wheels you see in watermills, when you open the tap water will flow from the pump and push the wheel into motion. Now in this simple hydraulic system two parameters are important: the pressure of the water (this is given from how powerful is the pump) and the amount of water that will flow in the pipes (this depends from the size of the pipes and the resistance that the wheel will oppose to the stream of water hitting it).You quickly understand that if you want the wheel to spin faster you need to increase the size of the pipes (but this works only up to a point) and increase the pressure that the pump can achieve. Increasing the size of the pipes allows more flow of water to go through them, effectively by making them bigger we have reduced the resistance they oppose to the flow of water. This works until a certain point where the wheel wonâ€™t spin any faster because the pressure of the water is not strong enough and this is when we need the pump to be stronger.
This can go on until the point when the wheel falls apart because the water flow is too strong and destroys it. Another thing you will notice is that as the wheel spins the axle will heat up a little bit, this is because no matter how good is the way we have mounted the wheel the attrition between the axle and the holes it is mounted in will generate heat. This is important to understand that in a system like this not all the energy you pump into the system will be converted into movement, some will be lost in a number of inefficiencies and will generally show up as heat emanating from some parts of the system.
So what are the important parts of the system as we described it before? The pressure produced by the pump is one, the resistance that the pipes and wheel oppose to the flow of water and the actual flow of water (letâ€™s say that this is represented by the number of litres of water that flow in one second) are the others.
Without going into much details electricity works a bit like water, you have a kind of pump (any source of electricity like a battery or a wall plug) pushes electric charges (imagine them like â€œdropsâ€ of electricity) down pipes represented by the wires where some devices are able to use them to produce heat (your grandmaâ€™s thermal blanket) light (your bedroomâ€™s lamp) sound (your stereo) movement (your fan) and much more.
So when you read on a battery 9V you can imagine the Voltage of the battery like the water pressure that can be potentially produced by this little â€œpumpâ€. This is measured in Volts from Alessandro Volta, the inventor of the first battery.
The flow of water has got and electric equivalent called â€œcurrentâ€ that is measured in Amperes from Andre Marie Ampere. Finally the resistance opposed to the flow of current by any means it travels through is called, yes you guessed right, resistance and itâ€™s measured in Ohms from the German physicist Ohm.
Mr ohm is also responsible for coming up with the most important law in electricity and the only formula you will really need to remember.
He was able to demonstrate that in a circuit the Voltage, the Current and the Resistance are all related to each other and in particular that the resistance opposed by the circuits determines the amount of current that will flow through it give a certain supply voltage.
Itâ€™s very intuitive if you think about it: Take a 9V battery and plug it into a simple circuit while measuring current, you will find that the more resistors you add to the circuit the less current will travel through it. Going back to the water flowing in pipes, given a certain pump if I place a tap (which we can assimilate to a variable resistor in electricity) the more I close the tap, increasing resistance to water flow, less water will flow through the pipes. Mr Ohm summarised his law into this formulas:
R (resistance) = V (voltage) / I (current)
V = R * I
I = V / R
This is the only rule that you really have to memorise and learn to use, because in most of your work this will be the only one you will really need.
Read more:The History of Eletricity
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