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

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 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:

ECG
ECG

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.

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Additional Activities

Capacitance True or False Exercise

Check your knowledge of the lesson about the definition and examples of capacitance by determining whether the following statements are true or false.

Directions

Print the following questions on a blank paper and underline or round the answer.


1. Capacitance is inversely proportional to voltage and is expressed in terms of coulombs.

True | False

2. A 10-farad capacitor connected to a 12-volt battery can store a charge of 100 coulombs.

True | False

3. In the human body, the cell membrane serves as the dielectric.

True | False

4. Protons flow towards the positive terminal of the battery and away from the negative terminal.

True | False

5. Rubber is a good example of a dielectric material.

True | False

6. A nerve cell may store electrical energy and release it as an impulse.

True | False

7. The conducting material sandwiched between two plates of a capacitor is known as a dielectric.

True | False

8. The two metal plates of a capacitor will be positively charged when connected across a battery.

True | False

9. The voltage source, such as a battery, can generate an electric field in a capacitor.

True | False

10. A capacitor that stores 12 coulombs of charge connected to a 3-volt battery can produce a capacitance of 4 farads.

True | False


Answer Key

1. False, because the correct statement is, "Capacitance is directly proportional to voltage and is expressed in terms of farads".

2. False, because the correct statement is, "A 10-farad capacitor connected to a 12-volt battery can store a charge of 120 coulombs".

3. True

4. False, because the correct statement is, "Electrons flow towards the positive terminal of the battery and away from the negative terminal".

5. True

6. True

7. False, because the correct statement is, "An insulating material sandwiched between two conducting plates of a capacitor is known as a dielectric".

8.False, because the correct statement is, "One plate of the capacitor is positively charged while the other one is negatively charged when connected across a battery".

9.True

10. True

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