A few quick conceptual questions about capacitators and dielectrics

AI Thread Summary
An electron placed between two plates of a parallel plate capacitor, with one at 0V and the other at 50V, will move towards the 0V plate due to the electric potential difference. When a dielectric is inserted into a charged, isolated capacitor, the charge remains constant because there is no external pathway for it to change, but the voltage will drop as the dielectric reduces the electric field. If the capacitor is connected to a battery, the voltage remains constant while the charge increases, as the battery compensates for the energy stored in the dielectric's displacement field. The discussion highlights the behavior of charges in electric fields and the effects of dielectrics on capacitors. Understanding these concepts is crucial for grasping the fundamentals of capacitors and dielectrics in electrical engineering.
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Homework Statement


So my question is conceptual. I am trying to figure out in what direction an electron will move if it starts between two plates of a parallel plate capacitator. One of the plates is at 0V and the other is at 50V.

Also, would placing a dielectric in a charged, isolated capacitator change its voltage but not charge?


The Attempt at a Solution


I know the 100 V plate would repel a negative charge. I would think the electron would move towards the 0V plate just because that is the way a capacitator is supposed to work (moving across an electric potential). Is this correct?

For the second question, I think charge wouldn't change when adding a dielectric in an isolated capacitator because there would be nowhere for the charge to go. But then the voltage would drop? Can someone verify that I am understanding this correctly?
 
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If you insert a dialectic into the capacitor, the dialectic will produce an induced electric field called the "displacement" field. This field acts to reduce the net field in the volume of the dialectic. If the capacitor voltage is not held constant by a battery or some other source, then yes the voltage will drop, but the charge will remain constant.

If the voltage is supplied by some battery, then the voltage will remain constant, but the energy stored in the capacitor will increase. This is because the displacement field has energy, and maintaining the potential forces the battery to do extra work by adding more charges to the plate.
 
recall that because of history, we are stuck with positive test charges

a positive test charge will want to move to the decreasing potential, this would be from 50 to 0

therefore, an electron would be the opposite, right?
 
Hmm okay, thanks for the responses!

My teacher wasn't too clear with wording the question, so I'm not sure if isolated means no voltage is being supplied... So if a battery was supplying voltage, the voltage would stay the same but the charge would increase to make potential stay the same?

Right, I forgot that only positive charges move across decreasing potential. That makes perfect sense now.
 
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