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What is Capacitance? - Definition, Equation & Examples

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  • 0:01 Definition of Capacitance
  • 0:39 Capacitors
  • 1:43 How to Calculate Capacitance
  • 2:19 Uses of Capacitors
  • 2:55 Capacitance & Human…
  • 3:41 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Capacitors are used to store and quickly release large amounts of electrical energy. In this lesson, we will learn how capacitors are created and used and how your body can function as a capacitor.

What is Capacitance?

Capacitance is the ability to store electrical energy. Almost all things, including you, can store some electrical energy and therefore have capacitance. When you rub your feet across a carpet, charged particles called electrons can be transferred from the carpet to you. When positive and negative charges are separated, the stored electrical energy increases. The charges you have picked up from the carpet give you electrical energy that you store until you touch something like a metal doorknob or another person that allows the energy to be released. You feel this as a mild shock as the energy leaves your body.

Capacitors

Although the ability to store some electrical energy is common, devices called capacitors are purposely designed to store large amounts of electrical energy. A typical capacitor consists of two conducting surfaces (usually metal plates) separated by an insulating material like air, rubber, or paper. This insulating material is called a dielectric.

In this parallel plate capacitor, two metal conducting plates are separated by a thin dielectric (electrical insulator)
capacitor

The capacitor can be charged by connecting one plate to the positive terminal of a battery and the other to the negative terminal. The electric field produced by the battery causes electrons to flow towards the positive terminal of the battery and away from the negative terminal. This causes the two capacitor plates to become charged. One will be positively charged and the other will be negatively charged. The insulating material keeps the charges from crossing over from one plate to the other and allows the capacitor to store electrical energy. If it is disconnected from the battery, the charges will remain stored in the capacitor until it is connected to another electric unit.

Some typical capacitors used in electric circuits
capacitors

How to Calculate Capacitance of a Capacitor

The capacitance of the capacitor tells you how much charge it can store when connected to a particular battery and is measured in units of farads. The capacitance (C) of a capacitor can be determined by measuring the amount of charge stored on each plate (Q) when it is connected to a battery with a certain voltage (V).

C = Q/V

For example, if we connected a capacitor to a 9 volt battery and measured that it stored 9 coulombs of charge, its capacitance would be 1 farad.

Uses of Capacitors

Capacitors are used in many devices that require electrical energy to be released quickly, like camera flashes and computer keyboards. They are also used in circuits that are designed to filter and amplify electronic signals. These circuits are found in radios, music amplifiers, and medical devices. Here's a more specific example of a medical device that uses capacitors:

This electrocardiogram (ECG) device measures the electric potential of the human heart. It uses capacitors to filter out other electrical signals so that the electrical activity of the heart can be monitored.
ECG

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