What Exactly Is Inside That Capacitor Inside Your Smartphone, Computer, Or Tesla?

Dec 09, 2023

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TJ McCue

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Most people who work with electricity have been shocked or zapped by it at some point in their career, but perhaps not as painfully as the inventor of the world’s first electrical capacitor in 1745. The Leiden (or Leyden) jar, invented by Dutch scientist Pieter van Musschenbroek, a professor of physics at Leiden University, was tested only once by the inventor personally.

NETHERLANDS — SEPTEMBER 15: The Leyden jar was an early capacitor, or a device for storing an electric charge. It was devised in 1746 by Pieter van Musschenbroek, at Leyden in the Netherlands. It is simply a glass jar with metal foil coatings inside and out. The inner coating can be connected to a source electric charge by a chain or other conductor. When one end of a discharger is placed in contact with the outer foil, and the other end is brought near the ball on top of the charged jar, a spark passes between the ball and the discharger. The Leyden jar is interesting because it produced much more powerful electric shocks, or sparks, than anything before it.

After receiving a powerful shock himself, van Musschenbroek, is said to have told a colleague “that the whole kingdom of France could not compel him to repeat the experience.” However, he went on to continue testing the device with a student, Andreas Cuneaus, who would accept the stored charge from the glass jar, partly filled with water, by intentionally touching the brass wire projecting out of the top while holding it in one hand. With early prototypes, it is estimated the jars could hold a charge between 20,000 and 60,000 volts.

Capacitors, and our ways for testing them, have thankfully come a long way since 1745. They come in all shapes and sizes, for a wide variety of purposes, but usually have the same basic components: Two conductors, known as plates, with an insulator portion between the plates, known as the dielectric.

The most common four capacitor types are named for their dielectric and reveal the materials they are made from. However, there are dozens of capacitor types, often hybrids of these four.