# Capacitor and Capacitance

## Introduction

Capacitors are small electronic components that can hold an electrical charge, and they’re commonly used in many different types of electrical devices and circuits, such as radios, TVs, microwaves, and computers. When you use capacitors in your electronics projects, you need to be aware of how they work and how they differ from other components like resistors and inductors.

## What is a Capacitor?

A capacitor is a two-terminal electrical component used to store energy in an electric field. This energy is stored as electric potential between its terminals, measured in volts. It consists of two electrical plates that are separated by a distance and this distance is filled with an insulating material.

The behavior of a capacitor depends on whether it is charging or discharging. During charging, current flows through a circuit into one terminal of a capacitor while at the same time charge builds up on each side of its other terminal (the electrolyte).

A voltage drop appears across terminals indicating that power is being converted into electrical energy. While discharging, the charge leaves one terminal and simultaneously builds up on both sides of its other terminal. Current flow stops when all available charges have left one terminal and equal but opposite charges build up on both sides of its other terminal (electrolyte).

## How Does a Capacitor Work?

A capacitor is a device used in electronics to store electric charge. Just like batteries, capacitors have an onside—the positive (+) pole—and an offside—the negative (-) pole. But unlike batteries, capacitors allow you to store an electrical charge without any chemical action or energy source being involved.

During the experiment, we apply the positive side of DC voltage to plate 1st and the negative side is connected to plate 2nd. When current flows in the capacitor, the plate 2nd becomes negative with respect to plat 1st. Current tries to flow from the positive plate of the capacitor to the negative plate. But current is unable to flow because of dielectric material.

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After some time, between plates of the capacitor store a limited amount of charge. After removing the battery, the charge accumulates between the two plates of the capacitor for a certain amount of time.

## How do you Determine the Value of Capacitance?

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The ability of a capacitor to hold an electrical charge is quantified by its capacitance. Plate 1st and 2nd of capacitors have +q and -q charge. We know that V is directly proportional to the electric field.

$\mathrm{Q\:\varpropto\:V}$

$\mathrm{Q \:= \:CV}$

$\mathrm{C \:= \:Q/V}$

### Energy Stored in Capacitor

Any circuit with a capacitor in it will have energy stored in it.

This energy is given by: E = 1/2 CV2

where

• C is capacitance,
• V is voltage and
• $\phi$V is potential difference (i.e. voltage).

A capacitor stores energy through an electrostatic field: unlike charge, which can flow from one point to another, electrostatic fields do not flow from one point of space to another.

### Standard Units of Capacitance

We major a capacitor in farad. But Farad is a large unit so we major it in sub-units like mili, nano, micro, etc.

• 1 μF (microfarad) =$\mathrm{10^{−6}\:F}$
• 1 mF (millifarad) = $\mathrm{10^{−3}\: F}$
• 1 pF (picofarad) = $\mathrm{10^{−12}\:F}$
• 1 nF (nanofarad) = $\mathrm{10^{−9}\: F}$

## Applications of Capacitors

• In electronics, capacitors are primarily used to block direct current while allowing alternating current to pass. In other words, capacitors act as an electric charge buffer in circuits. So, there are some applications of capacitors.

• Because of their ability to store energy in an electric field, capacitors are commonly used for filtering out unwanted frequency components or blocking transient voltages (e.g., voltage spikes) from damaging sensitive components in circuits.

• In addition, some types of capacitors can be used as timing elements in digital circuits like clocks because of their stable discharge characteristics.

• They can also be used as parts of resonant circuits (e.g., RC timing networks) or a parallel plate capacitor is often constructed on a printed circuit board as part of RF decoupling circuitry.

## FAQs

Q1. How do I Choose the Right One?

Ans: While there’s certainly no hard-and-fast rule for how many of each you need, some basic guidelines exist. First, try to estimate what percentage of your power will be DC (direct current), compared with AC (alternating current) or voltage spikes.

Q2. What is a variable capacitor?

Ans: A variable capacitor is a type of capacitor that can vary its capacitance, typically by rotating a control shaft or knob. Variable capacitors are used to tune radio frequency (RF) circuits, such as oscillators and filters. These capacitors are often in tandem with fixed capacitors, which serve as bandpass filters for separating signals at different frequencies; using variable capacitors makes it easier for an operator to adjust bandpasses precisely without guesswork.

Q3. What are Ultracapacitors?

Ans: Today, we’re going to take a look at another kind of capacitor, which is called an ultracapacitor. These types of capacitors are different from traditional electrolytic capacitors in that they work on a completely different principle.

Q4. What kind of energy is stored in a capacitor?

Ans: The capacitor is also capable of storing energy in an electrostatic field. So, instead of storing it as kinetic energy (in a rotating object, for example), or potential energy (in an elevated object), it stores it as electrostatic potential energy. At any given moment, a single charged capacitor has stored some amount of potential energy, which can be represented by that charge’s voltage multiplied by its capacitance.

Q5. Why dielectric is used in a capacitor as an insulating material instead of water?

Ans: Because water has low dielectric strength and a high dielectric constant. So, water will act as a conductor, and charges will leak through it.

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Updated on: 13-Oct-2022

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