I need i for a School Project, but I don’t quite understand when I search on google
In: Technology
As we know, positive charges repel other positive charges and attract negative charges. Negative charges likewise repel negative charges and attract positive charges.
Electronics tend to concern little with charges building up on objects, and this attraction/repulsion force beyond the interior of a wire. However, the electrons in one wire do put some force on the electrons in other nearby wires. The amount that they interact is the capacitance between the two.
A capacitor is designed so that the ‘wires’ are incredibly close together and have a lot of surface area almost in contact (but never actually in contact). This maximizes their capacitance.
Practically, what happens in a capacitor is that by adding some electrons to one side, electrons are much more content to leave the other side (due to the electrons in the first side repelling them). While electrons never actually cross the gap, it can seem as though they do since electrons flow in one side and out the other. This is, of course, not sustainable – it requires more and more voltage to move more and more electrons into that one side, but the higher the capacitance the more electrons can be moved before you need to raise the voltage.
When you have two thin metal plates separated by an insulator (even air) you can’t move electrons across the gap. You can crowd them, like when everybody crowds the platform waiting for the subway train to arrive (pre COVID). Since the train never comes, after a while you can open the gates and let all the electrons off the platform. Electrons can do this stupid fast, and nobody ever gets off the wires so it’s very efficient storage. Not big storage, like a chemical battery, but super fast.
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As electricity is difficult to visualise, it can be helpful to imagine a capacitor as a balloon sealed across a water pipe.
When you turn on the water then the balloon will begin to fill – like charging a capacitor. In a capacitor this charge is held using two different plates with a vacuum or dielectric material between them. The electrical field between the two means both plates will have equal and opposite charges.
Like in a balloon, current will continue to flow through the circuit – water continues to flow down the pipe. However, the progress of the water (or electrons in a circuit) are held back by the balloon/gap between plates.
At some stage the balloon bursts – or, in a capacitor the difference in charge becomes to great and the electricity travels across the vacuum/dielectric material, providing a boost of power greater than which could normally be provided by the circuit. This can be useful for things like compressors, motors, microwaves etc which require a larger starting current than it required to continuously run them.
This is also why capacitors retain charge after the circuit is disconnected from the power source, which can lead to shocks when touching even unplugged electronics.
You know how sometimes when you’re driving, people slow down to take pictures of traffic on the other side? Capacitance is kinda like that. It works because the electrons on one side are attracted to the other side and pile up. If you make the two sides closer together, more people will take pictures. If you make the material between the two sides more transparent, more people will take pictures. And if you make the traffic flow more congested, more people will take pictures.
Similarly, you can increase the amount of electricity stuck in a capacitor by decreasing the distance between the two sides, changing the material in the middle, or using more pressure (voltage) to cram more electricity in. This is where the analogy breaks down. Since electrons don’t take up any physical space, you can always cram more of them into a capacitor by increasing the voltage. You can’t really do that with cars.
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