How does a dielectric increase capacitance, conceptually.

In summary, a dielectric decreases the field strength of a capacitor, which causes the equilibrium voltage to change. This change in voltage allows more charge to be stored on the capacitor plate, which is due to the push from the battery.
  • #1
kcodon
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Hi all,

I'm a little stumped with how the dielectric increases capacitance. The general solutions all involve using the formulas, but don't really treat it conceptually. I realize that inserting a dielectric decreases field strength, and hence decreases the voltage across the capacitor. But if I have a capacitor in a DC circuit, then shouldn't the voltage across the capacitor remain the same, i.e. equal to the voltage of the cell? Then there would be no change in voltage (or charge) so no change in capacitance? This should be easy to test, unfortunately I lack a voltmeter or a capacitor.

Any insight would be appreciated,

Kcodon
 
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  • #2
kcodon said:
But if I have a capacitor in a DC circuit, then shouldn't the voltage across the capacitor remain the same, i.e. equal to the voltage of the cell? Then there would be no change in voltage (or charge) so no change in capacitance?

Yes, the equilibrium voltage should not change, that means that the amount of charge must change. C=Q/V, so capacitance is a measure of "charge storing" or "charge separating" ability. A big capacitor can store more charge for the same voltage.
 
  • #3
atyy said:
Yes, the equilibrium voltage should not change, that means that the amount of charge must change.

But I believe the reason for only a certain amount of charge being stored on a plate of the capacitor is that as charge builds up on the plate it gets to a point where all the accumulated charge repels any additional charge, with an "force" equal and opposite to that provided by the cell voltage. I don't think it is linked to the electric field across the plates So how does more charge accumulate when there isn't a greater voltage to "squeeze" it onto the plates?
 
  • #4
kcodon said:
I don't think it is linked to the electric field across the plates

It is intimately linked to the electric field between the plates. But we can also work with your picture. Like charges accumulate on the capacitor plate because of push from the battery. But they also don't want to accumulate on the capacitor plate because they are squeezed with each other. And those two balance. So if you put a dielectric in the middle, you are providing more opposite charge near the like charges, so the like charges are not so unhappy about being squeezed, and the same voltage can push more charge onto the capacitor plate.

Edit: I assumed you know the picture about the dielectric being polarized: http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/dielec.html.
 
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  • #5
atyy said:
So if you put a dielectric in the middle, you are providing more opposite charge near the like charges, so the like charges are not so unhappy about being squeezed, and the same voltage can push more charge onto the capacitor plate.

Thanks so much atyy, this is the little explanation I have been looking for all along! I love the little lightbulb moments like this, even if it is someone else that turns the bulb on!

Thanks again,

Kcodon
 

1. How does a dielectric material increase capacitance?

A dielectric material is an insulating material that is placed between the plates of a capacitor. When an electric field is applied, the molecules in the dielectric align themselves with the field, which creates an additional electric field that is opposite in direction to the applied field. This results in a decrease in the overall electric field between the plates, leading to an increase in capacitance.

2. Why is capacitance increased by using a dielectric material?

The presence of a dielectric material between the plates of a capacitor reduces the electric field, which in turn reduces the potential difference between the plates. As capacitance is directly proportional to the potential difference, the decrease in potential difference leads to an increase in capacitance.

3. What is the relationship between dielectric constant and capacitance?

The dielectric constant is a measure of how much a material can reduce the electric field between the plates of a capacitor. It is directly proportional to the capacitance, meaning that a higher dielectric constant results in a higher capacitance.

4. How does the thickness of the dielectric material affect capacitance?

The thickness of the dielectric material has an inverse relationship with capacitance. As the thickness increases, the electric field between the plates decreases, leading to an increase in capacitance. However, if the dielectric material becomes too thick, it may not be able to withstand the electric field and can result in breakdown of the capacitor.

5. Can any material be used as a dielectric?

No, not all materials can be used as a dielectric. A good dielectric material should have high insulation properties, low electrical conductivity, and be able to withstand high electric fields without breaking down. Some common dielectric materials include air, paper, glass, and plastic.

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