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In most capacitors, a
non-conducting material

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is placed between
the two metal pieces

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that make up that capacitor.

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There's two reasons for this.

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For one, the
non-conducting material

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prevents the pieces of metal
from touching each other, which

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is important because if the
pieces of metal were touching,

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no charge would ever
get stored since you've

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completed the circuit.

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But there's another
bonus to inserting

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a non-conducting material
between the plates

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of a capacitor.

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It will always increase the
capacitance of that capacitor.

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As long as the material
is non-conducting,

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it doesn't even
matter what it is.

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As long as you don't change
the area or separation

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between the plates, inserting
a non-conducting material

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will always increase
the capacitance.

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The name we give to
non-conducting materials

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place between capacitor
plates is a dielectric.

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But why does a dielectric
increase the capacitance?

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To find out, let's
look at this example.

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When you hook up a battery
of voltage V to a capacitor,

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charge will get separated.

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Now let's say you
remove the battery.

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The charge is stuck on the
plate since the negatives don't

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have a path in which to
get back to the positives.

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So even after
removing the battery,

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the charge on the plates is
going to remain the same.

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And the voltage will
also remain the same

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as the voltage of the
battery that charged it up.

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Now imagine placing a
dielectric in between the plates

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of the capacitor.

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The dielectric material is made
out of atoms and molecules,

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and when placed in between
the plates of this charged

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up capacitor, the negative
charges in the dielectric

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are going to get attracted
to the positive plate

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of the capacitor.

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But those negatives can't
travel to the positive plate

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since this dielectric is
a non-conducting material.

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However, the negatives
can shift or lean

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towards the positive plate.

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This causes the charge in
the atoms and molecules

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within the dielectric
to become polarized.

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To put it another way, the atom
kind of stretches and one end

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becomes overall negative
and the other end

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becomes overall positive.

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It's also possible that the
dielectric material started off

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polarized because some molecules
are just naturally polarized

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like water.

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In this case, when
the dielectric

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is placed between the
charged up capacitor plates,

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the attraction between
the negative side

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of the polarized molecule
and the positive plate

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of the capacitor would cause
the polarized molecules

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to rotate, allowing
the negatives to be

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a little bit closer to the
positively charged capacitor

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plate.

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Either way, the end result is
that the negatives in the atoms

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and molecules are going to face
the positive capacitor plate

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and the positives in
the atoms and molecules

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are going to face the
negative capacitor plate.

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So how does this
increase the capacitance?

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The reason this
increases the capacitance

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is because it reduces the
voltage between the capacitor

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plates.

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It reduces the voltage because
even though there's still just

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as many charges on
the capacitor plates,

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their contribution to the
voltage across the plates is

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being partially cancelled.

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In other words, some
of the positive charges

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on the capacitor plate are
having their contribution

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to the voltage
negated by the fact

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that there's a negative
charge right next to them now.

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Similarly, on the
negative side there's

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just as much negative
charge as there ever was,

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but some of the negative charges
are having their contribution

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to the voltage
canceled by the fact

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that there's a positive
charge right next to them.

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So the total charge
on this capacitor

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has remained the same, but
the voltage across the plates

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has been decreased because
of the polarization

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of the dielectric.

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If we look at the
definition of capacitance,

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we see that if the
charge stays the same

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and the voltage
decreases, the capacitance

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is going to increase,
because dividing

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by a smaller number
for the voltage

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is going to result in a larger
value for the capacitance.

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So inserting a
dielectric in this case,

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increase the capacitance
by lowering the voltage.

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Let's look at another case
of inserting a dielectric.

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Imagine we, again, let
a battery of voltage V

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fully charge this capacitor.

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And let's insert a dielectric
between the plates.

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But this time, let's leave
the battery connected.

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Now what's going to happen?

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Well, just like before,
the atoms and molecules

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in the dielectric are going to
stretch and orient themselves

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so that the negatives are
facing the positive plate

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and the positives are facing
the negative plate, which again

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reduces the voltage between
the two capacitor plates.

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But remember, we left
the battery connected

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and this battery is going
to try to do whatever

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it has to do in order
to make sure the voltage

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across the capacitor is the same
as the voltage of the battery

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V. Because that's just
what batteries do.

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They try to maintain
a constant voltage.

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So since the dielectric
reduced the voltage

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by canceling the contributions
from some of the charges,

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the battery's just going to
cause even more charges to get

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separated until the voltage
across the capacitor

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is again the same as the
voltage of the battery.

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So the charge stored on the
capacitor is going to increase,

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but the voltage is
going to stay the same.

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Looking at the definition
of capacitance,

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the charge on the
capacitor increased

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after we inserted
the dielectric.

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But the voltage across
the capacitor plates

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stayed the same,
since it's still

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hooked up to the same battery.

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So the effect of inserting
a dielectric again

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is to increase the
capacitance, this time

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by storing more charge for
the same amount of voltage.

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To figure out how much you've
increased the capacitance,

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you just need to know what's
called the dielectric constant

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of the material that you've
inserted between the capacitor

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plates.

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The dielectric constant is often
represented with a Greek letter

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kappa or simply a K.

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The formula for finding
out how the dielectric will

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change the
capacitance is simple.

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If the capacitance of a
capacitor before inserting

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a dielectric was C,
then the capacitance

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after inserting a dielectric
is just going to be k times C.

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We should note that
since a dielectric always

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increases the capacitance,
the dielectric constant k

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for a non-conducting material
is always greater than 1.

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So for example, if a capacitor
as a capacitance of 4

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farads, when you insert
a dialect with dielectric

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constant 3, the capacitance
will become 12 farads.

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