How Capacitors Work
A capacitor is somewhat similar to a battery. While they function in entirely different ways, both store electrical energy. If you’ve read about how batteries work, you know that a battery has two terminals. Inside, chemical reactions generate electrons at one terminal, while the other terminal absorbs them when a circuit is formed. In contrast, a capacitor is much simpler; it doesn’t create new electrons but merely stores them. It’s called a capacitor because it has the “capacity” to hold energy.
In this article, we will explore what a capacitor is, what it does, and how it is used in electronics. We’ll also delve into the history of capacitors and the contributions of several individuals in its development. Capacitors can be made for various purposes, from tiny plastic capacitors in calculators to ultra-capacitors that power commuter buses. Here are some types of capacitors and their applications:
- Air: Often found in radio tuning circuits.
- Mylar: Commonly used in timer circuits, like clocks, alarms, and counters.
- Glass: Suitable for high-voltage applications.
- Ceramic: Used for high-frequency purposes, such as antennas, X-ray machines, and MRI machines.
- Super Capacitor: Powers electric and hybrid vehicles.
Inside a Capacitor
Inside a capacitor, you’ll find two metal plates connected to terminals, separated by a non-conductive substance known as a dielectric. You can easily create a simple capacitor using two pieces of aluminum foil and a piece of paper, along with some electrical clips. While it won’t be the best capacitor in terms of storage capacity, it will definitely work.
Theoretically, any non-conductive material can serve as a dielectric. However, in practice, specific materials are chosen to best suit the capacitor’s intended use. Some common non-conductive materials include mica, ceramic, cellulose, porcelain, Mylar, Teflon, and even air. The type of dielectric determines what kind of capacitor it is and what it’s most suitable for. Depending on the size and type of dielectric, some capacitors excel in high-frequency applications, while others are better for high-voltage uses.
Capacitor Circuit
When you connect a capacitor to a battery, here’s what happens:
The plate connected to the negative terminal of the battery takes in electrons produced by the battery.
The plate attached to the positive terminal loses electrons back to the battery.
Once charged, the capacitor matches the voltage of the battery (for example, 1.5 volts from the battery means 1.5 volts on the capacitor). Small capacitors have limited capacity, but larger ones can hold a significant charge. You might even find capacitors as big as soda cans that can power a flashlight for a minute or more.
Even nature demonstrates how capacitors work through lightning. One plate is the cloud, the other is the ground, and the lightning is the charge that releases between these two “plates.” Clearly, such a large capacitor can hold an enormous charge!
Capacitor in Action
Imagine you have a battery, a light bulb, and a capacitor. If the capacitor is fairly large, here’s what happens: when you connect the battery, the light bulb will light up as current flows from the battery to the capacitor, charging it. The bulb will gradually get dimmer and eventually go out once the capacitor is fully charged.
If you then disconnect the battery and connect a wire instead, current will flow from one plate of the capacitor to the other. The bulb will shine brightly at first, then dim as the capacitor discharges, until it finally goes out completely.
In the next section, we’ll explore capacitance in more detail and look at the various ways capacitors are used.
History of the Capacitor
The invention of the capacitor has different stories depending on whom you ask. Records show that a German scientist named Ewald Georg von Kleist invented the capacitor in November 1745. A few months later, Pieter van Musschenbroek, a Dutch professor at the University of Leyden, created a similar device known as the Leyden jar, which is often credited as the first capacitor. Kleist didn’t have detailed records or the recognition that his Dutch counterpart received, so he’s frequently overlooked in the history of capacitors. However, both are now given equal credit, as it’s clear their discoveries were independent and coincidental.
The Leyden jar was quite simple. It was a glass jar half-filled with water and lined with metal foil both inside and out. The glass served as the dielectric, though it was once believed that water was the essential component. A metal wire or chain was often pushed through a cork at the top of the jar, connected to a charge source, typically a hand-cranked static generator. Once charged, the jar would hold two equal but opposite charges until connected by a wire, creating a small spark or shock.
Benjamin Franklin experimented with the Leyden jar and discovered that a flat piece of glass could work just as well, leading him to develop the flat capacitor, also known as the Franklin square. Years later, the English chemist Michael Faraday advanced the practical applications of capacitors by trying to store unused electrons from his experiments. This work led to the first usable capacitor, made from large oil barrels. Faraday’s innovations in capacitors ultimately allowed for the transmission of electric power over long distances. Thanks to his contributions, the unit of measurement for capacitors, or capacitance, became known as the farad.
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