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Fixed & Variable Capacitors: Parts & Types

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Instructor
Matthew Bergstresser

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

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

Capacitors are devices used to store electrical energy. Explore the parts and types of fixed and variable capacitors. Learn about capacitor anatomy and review capacitors in DC circuits, including series and parallel. Updated: 11/27/2021

Capacitor Anatomy

You probably use capacitors every day of your life. For example, if you typed on a keyboard to get to this lesson, guess what? You just 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.

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  • 0:04 Capacitor Anatomy
  • 1:08 Fixed Capacitors
  • 3:01 Variable Capacitors
  • 4:32 Capacitors in DC Circuits
  • 5:48 Lesson Summary
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Fixed Capacitors

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

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

Variable Capacitors

Variable capacitors are pretty much just as they're named. They're capacitors whose capacitance can change by physically or electronically moving the plates.

1. Tuning

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.

2. Trimmer

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.

3. Mechanical

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're mechanical, they are reliable because they aren't overly complicated.

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Practice:
Fixed & Variable Capacitors: Parts & Types Quiz

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Additional Activities

Fill-in-the-Blank Activity

This activity will help you assess your knowledge of fixed and variable capacitors.

Guidelines

For this activity, print or copy this page on a blank piece of paper. Then, use the words presented in the word bank to complete each of the given sentences. Neatly write your answers on the appropriate blank space provided.

Word Bank


Sentences

1. The ability to store electric charge which is measured in units of Farad is called __________.

2. An __________ uses aluminum oxide sheets acting as a dielectric and is deemed valuable for its large capacitance ability.

3. __________ are variable capacitors that are used in radios to listen or receive radio frequencies.

4. A DC circuit is considered to be __________ when there is only one direction for current to flow.

5. A piece of equipment is calibrated with the use of __________ after it has been manufactured.

6. Capacitors are separated by a non-conducting material called a __________.

7. When there are multiple paths that current could go through, a DC circuit is considered to be __________.

8. __________ are advantageous in applications to multi-meters that measure voltage, amperage, and resistance, for they change their capacitance by changing the DC voltage, applied to them.


Answer Key

1. capacitance

2. electrolytic capacitor

3. Tuning capacitors

4. series

5. trimmer capacitors

6. dielectric

7. parallel

8. Electronic capacitors

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