Fixed & Variable Capacitors: Parts & Types

Instructor: Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

Capacitors are devices that store electrical energy. In this lesson, we will explore the various types of capacitors, how they work, and how to calculate equivalent capacitance.

Capacitor Anatomy

You probably use capacitors every day of your life. If you typed on a keyboard to get to the this lesson, you used a capacitor. Want to know how it works? Let's see.

A capacitor is basically two conducting surfaces that are parallel to each other, either separated by air or another non-conducting material called a dielectric, and connected to a voltage source. Capacitance is the ability to store electric charge, and its unit is the farad (F). The use of a dielectric is to increase the capacitance of a capacitor.


The voltage source connected to the capacitor charges one plate with positive charge, and the other with negative charge. A capacitor is essentially what a battery is, but when the plates touch, the stored electrical energy is dissipated instantaneously, while a battery's energy is dissipated gradually. The change in the capacitance while pressing the key on the keyboard is translated by the computer into letters on the screen.

Fixed Capacitors

There are five types of fixed capacitors. A fixed capacitor is one where the conducting surfaces are not adjustable. Let's go through the types of fixed capacitors.

Paper Capacitors

Paper capacitors have paper as their dielectric material. Paper, covered in wax, is alternately layered between aluminum sheets, and rolled into a cylinder. Two wires are added, one to each end of the capacitor to connect to the voltage source. The advantages of paper capacitors is that they can be used in high voltage, and high amperage applications.

Plastic Capacitors

Various forms of plastic are used as dielectrics in plastic capacitors. There are two types of plastic capacitors: film foil, and metalized film. These capacitors are advantageous in situations where high insulation and high efficiency is required.

Ceramic Capacitors

Ceramic capacitors have a large charge to size ratio. A lot of charge in a small capacitor is advantageous where space is limited, and ceramic material is a good insulator.

Mica Capacitors

Mica capacitors are stable, reliable and can handle low to high voltages. There are two types of mica capacitors: stacked mica capacitors, and silver-mica capacitors. Layers of plain mica, or silver coated mica are sandwiched between thin sheets of aluminum or copper.

Electrolytic Capacitors

Electrolytic capacitors are advantageous because of their large capacitance capability. Between their conducting sheets, they have aluminum oxide sheets acting as a dielectric, and paper soaked with electrolytic fluid that acts as a conductor.

Various electrolytic capacitors

Variable Capacitors

Variable capacitors are pretty much just as they are named, their capacitance can change by physically or electronically moving the plates.


Tuning capacitors are commonly used in radios where you tune into a radio station. Originally, radios had a knob that could be turned changing the distance between the capacitor's plates.


Trimmer capacitors are used in the calibration of equipment after it has been manufactured. They are commonly located on printed circuit boards, and if there is any variation in their capacitance over time, they can be adjusted, but they are only designed to be able to handle a few adjustments. They commonly hold 100 volts, but some can go up to 300 volts.


Mechanical capacitors have a series of semi-circular plates inside of them attached to a knob. The advantage of this is that the capacitance can be changed quickly if needed, and since they are mechanical, they are reliable because there aren't overly complicated.

Variable capacitor


Electronic capacitors change their capacitance by changing the DC voltage applied to them, which is an advantage in certain applications such as multi-meters that measure voltage, amperage and resistance. DC stands for ''direct current'', which is the type of current provided by a battery.

Capacitors in DC Circuits

As previously mentioned, capacitors store electrical energy. There are two types of basic DC circuits: series, and parallel. Series circuits only have one direction for current to flow, and parallel circuits cause the current to go through multiple paths.

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