Ph272A Students’ questions #4
Capacitor, capacitance, energy stored
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Q: What causes the electron flow to stop?
A: The flow of electrons eventually stops when no more work can be done in storing them in the
capacitor because it is fully charged.
Questions:
1. Is it possible to calculate the capacitance of a parallel-plate capacitor if the two plates do not
have the same shape/size? For example, if a rectangular plate and a circular plate set up as a
parallel-plate capacitor and have a potential difference across them, can you find out the
capacitance even though the shapes of the plates are different?
2. How is energy "stored" in an electric field?
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Q. Can a capacitor made of two insulators separated by a distance? Why
or Why not? A capacitor can not be made of two insulators separated
by a distance because the charges need to be able to move freely
through the material, and insulators do not allow charges to freely
flow.
1. Why is electrostatic potential energy stored in the electric field
that is present between the two plates, and how does this change when
the distance between changes?
2. In sample problem 30-9, pg. 690, why is the negative present? Could
you please show the E of the gaussian surface?
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Q. What causes the electron flow to stop?
A. The potential difference between the plates is the same as the
potential difference between the battery terminals. No more charge
can be added because they are at the same potential.
1) Can you explain how dielectrics affect charges? How can it
increase the performance of a capacitor, doesn't it restrict charge?
2) Can you explain how energy is stored in an electric field? Like
how is it stored in the volume between the plates and what keeps it
there.
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Q. What causes the electron flow to stop? A battery maintains a
constant potential difference between its terminals so when it reaches
that constant, electron flow stops.
Q. If the plates recieve a charge of equal density, would this change
if the platers were different sizes/shapes?
Q. Would materials put between the two terminals affect the capacitor?
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They talk about this thing called the "path of integration (p. 681,
bottom)" what is this? Does it only affect the distance that you
integrate for?
The book also stated that you can use capacitors of any shape (p. 679).
How would you calculate the capacitance (C) for such capacitors? Does
it simply depend on electric field configurations?
(Q. Can a capacitor made of two insulators separated by a distance? Why
or Why not?)
I don't think insulators can make capacitors. I mean, capacitors need
to give off an electric field in order to cause electron flow and do
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their job, and an insulator is not designed to do that, in fact, they
do quite the opposite by keeping electrons from flowing.
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q)flow of electrons will stop because a charge +q appears on on plate
of the capacitor a charge -q appears on the other plate. these charges
are equal in magnitude but opposite in direction so and equilibrium is
created and the electron flow stops.
1) are the plates for a capacitor always perfectly parallel. if not
what happens if they intersect or touch.
2)can you give some examples of dielectric materials, and where they
might be used.
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Q. What causes the electron flow to stop?
The electron flow stops because the plate in the capacitor aren't connected and the capacitor is
being charged. How do capacitors release their charge?
Why would it be important to find the enery density of a capacitor?
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Q. Can a capacitor made of two insulators separated by a distance? Why
or Why not?
A capacitor cannot be made with two insulating materials because a
capacitor needs to store energy as an electrostatic field and because
insulators are unable to accept charges or allow electrons to flow
1. does the shape in which a capcitor is designed changed its
effectiveness to store energy?
2. In a capacitor does the energy stored as an electric field get
weaker over tme?
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Here are my two questions from chapter 30.
30-1)
How is a capacitor able to release stored energy rapidly?
30-2)
If the equation for capacitance is , then does that mean every capacitor has an infinite range of
charge that it can store (if there were to be infinite potential difference in a battery)? Is there a
limit to the amount of charge a capacitor can store?
Here is my attempt at one answer.
Q. What causes the electron flow to stop?
The electron flow stops in a capacitor because the potential difference in the capacitor's parallel
plates is equal to the potential difference across the terminals of the battery.
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