Shiken premium Upgrade Banner

If you're interested in electronics, you may have heard of a capacitor. It's a handy little device that can store electricity and keep your circuits safe from sudden surges. Some people might wonder, "Isn't that what a battery does?" Well, not exactly. See, batteries store energy chemically, while capacitors store it electrically. Plus, capacitors can't hold a charge as long as batteries can because they lose energy faster. That's why it's important to choose the right one for your project, depending on what you need it for. And that's where capacitance comes in!

A Capacitor

The fast movement of electrons between the two plates of a capacitor makes it very useful in electronic applications.


A capacitor is made up of two metal plates that are separated by an insulating material called a dielectric. The plates are usually made of aluminium, which is a type of metal that conducts electricity. The dielectric is an important part of the capacitor because it helps to store electric charges.

But before we can understand how a capacitor works, we need to know about something called polarisation. This is when polar molecules in the dielectric line up in a certain way. These molecules have a positive and a negative end, so they can be attracted to opposite charges.

When there's no charge in the capacitor, the polar molecules in the dielectric are randomly scattered. But when the capacitor is charged, the molecules line up in a way that creates an electric field. This field is what allows the capacitor to store and release electric energy. And that's how polarisation plays a role in the workings of a capacitor.

Random molecules (top) and molecules in an electric field (bottom)

When a voltage is applied to a capacitor, an electric field is generated. The positive ends of the molecules are attracted to the negatively charged plate and vice versa. As the dielectric is an insulator and the molecules cannot shift, the polarised molecules orient themselves in such a way that opposite charges on the molecules and the plates face each other.

Orientation of polarised molecules in an electric field
Orientation of polarised molecules in an electric field

When the polar molecules in the dielectric align themselves in a certain way, they create an electric field. This field is in the opposite direction to the capacitor plates, which reduces the potential difference. As a result, the capacitor's ability to hold a charge per unit of potential difference increases.

To charge a capacitor, you can use a battery. Simply connect the negative end of the battery to the negative terminal of the capacitor, which is usually indicated by a strip or marking. Then, connect the positive end of the battery to the positive terminal. However, it's important to note that not all capacitors have marked poles. In that case, they can be connected in any direction in the circuit.

Symbol of a capacitor
Symbol of a capacitor

The charges flow from the battery to the negative terminal of the capacitor and from the positive plate to the positive end of the battery.

The diagram shows how the voltage across the plates and the current flow into the plates vary as the capacitor charges
The diagram shows how the voltage across the plates and the current flow into the plates vary as the capacitor charges

When a capacitor is charged, the electrons flow from the positive plate to the battery and from the battery to the negative plate. Once this flow is complete, no more electron flow is possible, and the capacitor becomes charged. One side of the capacitor becomes negatively charged while the other becomes positively charged. At this point, the capacitor is at the same voltage level as the battery.

The accumulation of electrons on one side of the capacitor means that it is storing energy. This energy can be released when it is needed, such as when the capacitor is connected to a circuit. When the capacitor is discharged, the energy is released and the electrons flow back to their original positions.

The potential difference between the plates of the capacitor is created by the difference in the number of charges on each plate. This difference in charge creates an electric field, which is what allows the capacitor to store energy. 

Application of a capacitor

Yes, a charged capacitor can be used to provide a charge in a circuit without any interruptions. A capacitor is an electrical component that stores energy in the form of an electric field. When a capacitor is connected to a circuit, it can store energy and then release it when needed. This is useful for providing a charge to a circuit without any interruptions, as the capacitor can act as a temporary battery. For example, when an LED is connected to a capacitor that is fully charged, the charges from the negative plate on the capacitor will flow through the LED to the positive plate on the capacitor until there is no potential difference between the two terminals. This will cause the LED to flash for a short period of time. If a is connected to the capacitor in this circuit, the capacitor will charge and store energy and then discharge it again if there is any interruption in the current flow.

Measuring the stored energy

There are two values on a capacitor, one showing the voltage (V) and the capacitance in Farads (F).

Capacitor with readings of voltage and capacitance
Capacitor with readings of voltage and capacitance

The voltage reading on the capacitor indicates the maximum voltage that it can handle. If that value is exceeded, the chances are that a capacitor might burn, sometimes even explode.

The capacitance of a capacitor

Every capacitor has a capacitance, which is its capacity to store electrical charge. The symbol for capacitance is C, which is measured in Farads. Farads are the number of coulombs that can be stored per volt:

Capacitance can, therefore, be used to calculate the charge in coulombs:

Q = electric charge.C = capacitance.V = voltage.

The capacitance formula

Yes, capacitance can be calculated using the equation:

C = epsilon nought * A / d

where C is capacitance measured in coulombs per volt (F), epsilon nought is the dielectric constant of free space (8.85 × 10⁻¹² F/m), A is the area of the plates measured in metres squared (m²), and d is the distance between the plates measured in metres (m).

Using the given values, we can calculate the capacitance of the parallel plate capacitor as follows:

C = (8.85 × 10⁻¹² F/m) * 0.525 m² / 2.15 × 10⁻³ m
C = 2.16 × 10⁻⁸ F

This may seem like a small capacitance value, but it is actually quite large in reality. Capacitors are used in a variety of electrical circuits to store and release energy, and their capacitance values can range from picofarads (10⁻¹² F) to farads (F), depending on the application.


What is capacitance? 

Capacitance is the ability of an object to store a charge.

How capacitance is calculated? 

Capacitance is calculated by calculating the charge per unit potential difference.

How is capacitance measured?

 Capacitance can be measured with a Digital Multimeter (DMM).

What is capacitance measured in? 

The units in which the capacitance is measured are Farads (F). 

What is the capacitance of a short-circuited capacitor? 

When a capacitor is short-circuited, the two plates act as one, and no dielectric medium exists between the two plates. Hence, the capacitance is 0.

Join Shiken For FREE

Gumbo Study Buddy

Explore More Subject Explanations

Try Shiken Premium
for Free

14-day free trial. Cancel anytime.
Get Started
Join 20,000+ learners worldwide.
The first 14 days are on us
96% of learners report x2 faster learning
Free hands-on onboarding & support
Cancel Anytime