Capacitors are widely used today in automotive circuits and systems. They are important for many reasons as they help with noise filtering in radios, reduce voltage spikes in a circuit, act a a short power supply, and act as a timer circuit in some automotive applications. In cars you will specifically find them in electronic ignition modules, output terminals of alternators, and armature of some starter motors.
Capacitors, well really capacitance, was first discovered all the way back in 1745 by scientists named Ewald Christian von Kliest and Pieter van Musschebroek. They made the discover of capacitance separately when they used what is know as a Leyden jar. This is basically just a jar filled with water, along with a nail stopper in the water, and a mechanical arm that touches the jar to conduct electricity. They both found when the nail was charged with electrical energy it could be stored. They found this out when they touched the nail and got an electric shock. Probably a bit of a surprised the first time they did the experiment.
While both of these scientists made an important discovery regarding capacitance, they are not credited with first building the capacitor. That honor goes to John Belvis in 1747 two years later. He put foil on the inside and outside of the Leyden jar building what is now considered the first capacitor in history.
How Capacitors Work
Capacitors consists of two conductive plates that are in parallel. Between them sits an insulating material such as plastic, paper, glass, ceramic, or mica. All these materials do not conduct electricity very well and are known as the dielectric. The dielectric in the Leyden jar would be the glass and jar itself. The strength of a capacitor is determined by the surface of the conductive plates, distance between them, and the dielectric material.
What happens is when a capacitor is placed in an electrical circuit the power source, a battery in vehicles, force electrons around the two capacitor plates since there is a dielectric in the middle. One plate becomes positively charged losing electrons as the negative plate is gaining electrons. Current continues to collect and flow around the capacitor until it reaches the voltage source. This means in essence a capacitor becomes like an extra charged battery in the circuit.
When the circuit is open the capacitor will hold a charge until some external source will discharge it. Theoretically it should be able to hold a charge but the energy stored in the capacitor will slowly drain over time. The better the dielectric, the worst it conducts electricity, the better it will hold a charge.
If a capacitor is connected in a parallel circuit it will increase the capacitance strength of that circuit. This is almost like making the surface area of the conductive plates larger as you are just adding more. If you want to decrease the capacitance you can put them in series circuit. Essentially this means you are placing the distance of capacitors farther apart therefore reducing the effectiveness.
Capacitors are used in many automotive applications and in electronics which includes televisions, computers, and more. Hopefully the next time you power something up you will think about the role capacitors play in your everyday life.