capacitancecapacitordielectric
My textbook is trying to explain why adding in a dielectric between two conductors causes a change in the field inside. They provide the following image:
I don't understand how the second image is equal to the third image. Why does polarization and alignments of the molecules create an electric field in the shown direction?
Dielectric polarization happens from polar molecules. The work done by an external field behaves like a charge, but unlike a electrons in a material, these charges cannot move. So if you had some dielectric material, you'd want to be able to find out what an external electric field does to it.
\$P_{pv}\$ is the bound charge, its locked up inside of the polar molecules, they aren't going to escape the material and move down a wire.
\$P_{ps}\$ is the surface charge. There could be charges on the surface, these need to be accounted for.
You add them both up and you know how much charge you have ( and what kind of useful things you can do with it like store energy)
My question is how does two diffrenet capacitor having same capacitance and footprint and voltage rating but only diffrent dielectric will affect my overall effect on circuit.
On some circuits it will have no affect and on some other circuits it may have a significant effect. Temperature of operation of your circuit can also play a part. On some circuits the better dielectric material of X7R still may not be good enough compared to going to C0G/NP0 dielectric.
So really, to answer this you have to look at your target circuit and ask yourself if the dielectric material is going to cause problems. Look at this picture below for an example of dielectric effects causing capacitor value changes versus temperature: -
And some dielectrics will modify the terminal capacitance depending on how much DC voltage is applied: -
Best Answer
The end is the net result. The blue and red dots in the middle of the second diagram "cancel out", so to speak. This results in the third diagram being an accurate model of the real physical situation in the second diagram.