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How does a capacitor work ??

The capacitor is the essential component of any

circuit design.

And in fact, after the resistor, it is the second most used passive component in the

circuits.

Now, these capacitors are available in various size and shapes.

But the basic function of any capacitor is to store the electrical energy.

So, now in this video, let's understand how does this capacitor work and how the energy is

stored across this capacitor.

Now, this capacitor consists of two conductive plates which are separated by a dielectric

material.

Now, this dielectric material is the insulating material and it opposes the flow of current.

So, now let's understand when we apply the voltage to this capacitor then how the energy

is stored across this capacitor.

Now, before the application of voltage, the two conducting plates of this capacitor are

electrically neutral.

It means that it has the equal amount of positive as well as the negative charge.

But once the voltage is applied to this capacitor, then from the top plate the electrons or the

negative charge is attracted towards the positive terminal of this battery.

And through the negative terminal of the battery, the electrons are pushed towards the bottom

plate of this capacitor.

Now, because of the dielectric material between the two plates electrons which are collected

at the bottom plate of this capacitor are not able to cross this barrier.

And because of that, you will observe that over the period of time the electrons will

get accumulated at the bottom plate of this capacitor.

So, over the period of time, the top plate will have a shortage of electrons, while the

bottom plate will have excessive electrons.

Or we can say that the top plate will get positively charged, while the bottom plate

will get negatively charged.

And because of the charged particles, the potential difference will get developed across

the two plates.

Now, the building of charges across the two plates will continue till the point the potential

difference that is developed across the two plates is equal to the supplied voltage.

Now, because of this potential difference, the electric field will get developed across

the two plates.

And this developed electric field is directly proportional to the potential difference and

it is inversely proportional to the distance between the two plates.

So, smaller the distance between the two plates, the stronger will be the electric field.

So, in this way, when we apply the voltage to the capacitor, then the charges are developed

across the two plates of this capacitor and because of the development of the charge,

the electric field is developed between the two plates.

So, in this way, the capacitor stores the energy in form of this electric field.

Now even if we remove this voltage source, then also the charges that are developed across

the two plates will remain as it is.

So, unless we apply the conductive path to this capacitor, the charges that are developed

across the two plates will remain as it is.

So, as you can see over here, the conductive path is connected between the two terminals

of this capacitor.

And load in the form of the bulb is connected to this conductive path.

So, now whenever we turn on this switch at that time, the electrons from the bottom plate

will get attracted towards the top plate.

And in this way, you will see the transfer of charge or flow of current through this

conductive path.

So, now because of the flow of current, you will see that the bulb will grow.

And in this way, the current will flow through this conductive path.

And this procedure will continue till both the plates will become electrically neutral.

So, over the period of time, you will observe that both plates will become electrically

neutral.

And there will not be any flow of electrons through this conductive path.

And because of that, the bulb will again turn off.

So, in this way, the charge that was developed across the capacitor has been discharged through

this conductive path.

And this phenomenon can be known as the discharging of the capacitor.

Now, the ability of the capacitor to store the charge is known as the capacitance.

And it is represented as the charge that is developed across the capacitor per unit voltage.

And generally, it is denoted by the unit of Farad.

Now, this farad is a very big unit and usually, it is not used to define the capacitance.

Rather very small units like mF, uF and pF are used to define the capacitance.

So, now for the given capacitance if you want to store the more charge across the capacitor

then you need to apply the more voltage across that capacitor.

Or for the given voltage suppose if you want to store the more charge across the capacitor,

then you need to select the capacitor in a such a way that it has a large capacitance.

So, as you can see over here, by changing the applied voltage we change the amount of

charge that is stored across the capacitor.

But here we can not increase the voltage indefinitely.

So, for every capacitor, you will find that the maximum voltage rating has been defined.

So, the voltage that is applied across the capacitor should be less than that maximum

rating.

So, if the applied voltage is greater than the maximum rated voltage, in that case, you

will see the dielectric breakdown in the capacitor.

So, now let's see the factors which affect the capacitance of this capacitor.

So, there are three factors which affect the capacitance of this capacitor.

The first is the area of the plates. then the second factor is the distance between

the two plates of this capacitor.

And the third factor is the permittivity of the dielectric material.

And the relation between three can be given by this expression.

That is C is equal to ε*A/d.

So, as you can see over here, the capacitance of this capacitor is directly proportional

to the area of the plate as well as the permittivity of this dielectric material.

And it is inversely proportional to the distance between the plates.

So, now let's see, how these factors can affect the capacitance of this capacitor.

So, the first factor is the area of these plates.

So, as the area of the plates increases, the amount of charge that can be stored across

the plates will also increase.

And in a way, we can say that the capacitance of the capacitor will increase.

Now, the second factor which affects the capacitance is the distance between the two plates.

So, now as the distance between the two plates reduces, the electric field that is developed

across the two plates will also increase.

Because it is inversely proportional to the electric field.

And as this electric field increases, the charge that can be stored across the capacitor

will also increase.

So, the third factor which affects the capacitance is the permittivity of the dielectric material.

Now, this permittivity can be defined as the product of absolute permittivity and the relative

permittivity.

Where this relative permittivity is also known as the dielectric constant of the material.

So, because of this dielectric material, the capacitance of the capacitor will increase.

So, now let's understand how this dielectric material affects the capacitance of the capacitor.

Now, like I said before, this dielectric material is the insulating material.

So, it will not allow the flow of current.

But this dielectric material has polar molecules.

It means that whenever there is no electric field, in that case, these molecules are aligned

randomly.

But whenever the external electric field is applied, in that case, these molecules aligned

themselves according to the electric field.

So, at the top edge of the dielectric material, if you see, you will find the negative charges.

While at the bottom end of this dielectric material you will find the positive charges.

Now, these charges develop its own electric field, which opposes the electric field that

is generated by the capacitor.

So, because of this dielectric material, the effective electric field of the capacitor

will reduce.

And in a way, we can say that the potential difference that is generated across the two

plates will also reduce, provided the charges that are developed across the two plates are

constant.

So, in that case, to increase the potential we require the more amount of charge across

the two plates.

So, in a way, we can say that, because of the introduction of this dielectric material,

the capacitor can more amount of charge.

Or we can say that the capacitance of the capacitor will increase.

So, these are the three factors which affect the capacitance of this capacitor.

So, I hope in this video, you understood how does the capacitor works and which are the

factors which affect the capacitance of the capacitor.

So, if you have any question or suggestion, do let me know in the comment section below.

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