Dielectric Constant

[MedPR]

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In a medium, F=k*q1*q2/K*(r^2), where K is the dielectric constant value.

So it makes sense that a small dielectric constant results in a larger force between the charges.

However, TBR also says "If the polarizability increases, then the dielectric constant increases."

Wouldn't a highly polar molecule exert more force on a neighboring polar molecule than a nonpolar (or less polar) molecule would? So shouldn't the dielectric constant decrease as polarizability increases?

 

[MT Headed]

In a medium, F=k*q1*q2/K*(r^2), where K is the dielectric constant value.

So it makes sense that a small dielectric constant results in a larger force between the charges.

However, TBR also says "If the polarizability increases, then the dielectric constant increases."

Wouldn't a highly polar molecule exert more force on a neighboring polar molecule than a nonpolar (or less polar) molecule would? So shouldn't the dielectric constant decrease as polarizability increases?

I see what you are trying to say, but the way to think about this is that the polarizable material orients itself backwards in the electric field, i.e. positive parts of the dialectric point to the negative part of the charged plate. Makes sense, yes?

Now think about what direction the electric field of the polarizable dialectric is creating as a whole... it's a new electric field pointing backwards in the middle of the original field. Thus it reduces all of the effects (like force) that you would expect to find in the field.

That's why a highly polarizable material has a high dialectric constant, and this causes the forces to go down.


You may have experienced this in lab, too. You have a capacitor, stick a polar dialectric in there, and its field goes down. Interestingly, you may also have seen the opposite in lab with magnets. You have a magnetic field, you stick something in the middle of it, like a bar of iron, and *blam* the magnetic field goes up!