How does a capacitor work

WEBVTT
Kind: captions
Language: en

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The
capacitor is the essential component of any
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circuit design.
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And in fact, after the resistor, it is the
second most used passive component in the
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circuits.
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Now, these capacitors are available in various
size and shapes.
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But the basic function of any capacitor is
to store the electrical energy.
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So, now in this video, let's understand how does
this capacitor work and how the energy is
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stored across this capacitor.
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Now, this capacitor consists of two conductive
plates which are separated by a dielectric
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material.
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Now, this dielectric material is the insulating
material and it opposes the flow of current.
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So, now let's understand when we apply the
voltage to this capacitor then how the energy
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is stored across this capacitor.
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Now, before the application of voltage, the
two conducting plates of this capacitor are
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electrically neutral.
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It means that it has the equal amount of positive
as well as the negative charge.
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But once the voltage is applied to this capacitor,
then from the top plate the electrons or the
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negative charge is attracted towards the positive
terminal of this battery.
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And through the negative terminal of the battery,
the electrons are pushed towards the bottom
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plate of this capacitor.
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Now, because of the dielectric material between
the two plates electrons which are collected
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at the bottom plate of this capacitor are
not able to cross this barrier.
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And because of that, you will observe that
over the period of time the electrons will
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get accumulated at the bottom plate of this
capacitor.
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So, over the period of time, the top plate
will have a shortage of electrons, while the
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bottom plate will have excessive electrons.
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Or we can say that the top plate will get
positively charged, while the bottom plate
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will get negatively charged.
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And because of the charged particles, the
potential difference will get developed across
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the two plates.
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Now, the building of charges across the two
plates will continue till the point the potential
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difference that is developed across the two
plates is equal to the supplied voltage.
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Now, because of this potential difference,
the electric field will get developed across
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And this developed electric field is directly
proportional to the potential difference and
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it is inversely proportional to the distance
between the two plates.
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So, smaller the distance between the two plates,
the stronger will be the electric field.
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So, in this way, when we apply the voltage
to the capacitor, then the charges are developed
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across the two plates of this capacitor and
because of the development of the charge,
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the electric field is developed between the
two plates.
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So, in this way, the capacitor stores the
energy in form of this electric field.
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Now even if we remove this voltage source,
then also the charges that are developed across
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the two plates will remain as it is.
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So, unless we apply the conductive path to
this capacitor, the charges that are developed
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across the two plates will remain as it is.
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So, as you can see over here, the conductive
path is connected between the two terminals
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of this capacitor.
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And load in the form of the bulb is connected
to this conductive path.
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So, now whenever we turn on this switch at
that time, the electrons from the bottom plate
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will get attracted towards the top plate.
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And in this way, you will see the transfer
of charge or flow of current through this
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conductive path.
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So, now because of the flow of current, you
will see that the bulb will grow.
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And in this way, the current will flow through
this conductive path.
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And this procedure will continue till both
the plates will become electrically neutral.
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So, over the period of time, you will observe
that both plates will become electrically
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neutral.
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And there will not be any flow of electrons
through this conductive path.
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And because of that, the bulb will again turn
off.
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So, in this way, the charge that was developed
across the capacitor has been discharged through
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And this phenomenon can be known as the discharging
of the capacitor.
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Now, the ability of the capacitor to store
the charge is known as the capacitance.
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And it is represented as the charge that is
developed across the capacitor per unit voltage.
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And generally, it is denoted by the unit of
Farad.
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Now, this farad is a very big unit and usually,
it is not used to define the capacitance.
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Rather very small units like mF, uF and pF
are used to define the capacitance.
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So, now for the given capacitance if you want
to store the more charge across the capacitor
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then you need to apply the more voltage across
that capacitor.
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Or for the given voltage suppose if you want
to store the more charge across the capacitor,
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then you need to select the capacitor in a
such a way that it has a large capacitance.
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So, as you can see over here, by changing
the applied voltage we change the amount of
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charge that is stored across the capacitor.
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But here we can not increase the voltage indefinitely.
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So, for every capacitor, you will find that
the maximum voltage rating has been defined.
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So, the voltage that is applied across the
capacitor should be less than that maximum
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rating.
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So, if the applied voltage is greater than
the maximum rated voltage, in that case, you
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will see the dielectric breakdown in the capacitor.
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So, now let's see the factors which affect
the capacitance of this capacitor.
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So, there are three factors which affect the
capacitance of this capacitor.
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The first is the area of the plates. then
the second factor is the distance between
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the two plates of this capacitor.
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And the third factor is the permittivity of
the dielectric material.
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And the relation between three can be given
by this expression.
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That is C is equal to ε*A/d.
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So, as you can see over here, the capacitance
of this capacitor is directly proportional
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to the area of the plate as well as the permittivity
of this dielectric material.
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And it is inversely proportional to the distance
between the plates.
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So, now let's see, how these factors can affect
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So, the first factor is the area of these
plates.
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So, as the area of the plates increases, the
amount of charge that can be stored across
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the plates will also increase.
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And in a way, we can say that the capacitance
of the capacitor will increase.
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Now, the second factor which affects the capacitance
is the distance between the two plates.
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So, now as the distance between the two plates
reduces, the electric field that is developed
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across the two plates will also increase.
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Because it is inversely proportional to the
electric field.
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And as this electric field increases, the
charge that can be stored across the capacitor
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will also increase.
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So, the third factor which affects the capacitance
is the permittivity of the dielectric material.
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Now, this permittivity can be defined as the
product of absolute permittivity and the relative
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permittivity.
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Where this relative permittivity is also known
as the dielectric constant of the material.
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So, because of this dielectric material, the
capacitance of the capacitor will increase.
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So, now let's understand how this dielectric
material affects the capacitance of the capacitor.
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Now, like I said before, this dielectric material
is the insulating material.
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So, it will not allow the flow of current.
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But this dielectric material has polar molecules.
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It means that whenever there is no electric
field, in that case, these molecules are aligned
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randomly.
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But whenever the external electric field is
applied, in that case, these molecules aligned
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themselves according to the electric field.
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So, at the top edge of the dielectric material,
if you see, you will find the negative charges.
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While at the bottom end of this dielectric
material you will find the positive charges.
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Now, these charges develop its own electric
field, which opposes the electric field that
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is generated by the capacitor.
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effective electric field of the capacitor
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will reduce.
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And in a way, we can say that the potential
difference that is generated across the two
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plates will also reduce, provided the charges
that are developed across the two plates are
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constant.
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So, in that case, to increase the potential
we require the more amount of charge across
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So, in a way, we can say that, because of
the introduction of this dielectric material,
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the capacitor can more amount of charge.
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Or we can say that the capacitance of the
capacitor will increase.
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So, these are the three factors which affect
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So, I hope in this video, you understood how
does the capacitor works and which are the
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factors which affect the capacitance of the
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So, if you have any question or suggestion,
do let me know in the comment section below.
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