Energy density of a capacitor

  • Thread starter baker265
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  • #1
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Homework Statement



A parallel-plate capacitor with C = 16 mu or micro FF is charged so as to contain 1.7 J of energy. If the capacitor has a vacuum between plates that are spaced by 0.35 mm, what is the energy density (the energy per unit volume)?

I am a little lost of this problem and have no idea if I'm doing it correctly. Am I ?

Homework Equations


v = A*d
E,density=U/v


The Attempt at a Solution


v=16e-3/.35e-3=45.71
E=1.7/45.71=.0371 J/m^3
 

Answers and Replies

  • #2
ehild
Homework Helper
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Homework Statement



A parallel-plate capacitor with C = 16 mu or micro FF is charged so as to contain 1.7 J of energy. If the capacitor has a vacuum between plates that are spaced by 0.35 mm, what is the energy density (the energy per unit volume)?

I am a little lost of this problem and have no idea if I'm doing it correctly. Am I ?

Homework Equations


v = A*d
E,density=U/v


The Attempt at a Solution


v=16e-3/.35e-3=45.71 ????
E=1.7/45.71=.0371 J/m^3

Is the capacitance 16 μF (microfarad)?

How do you calculate the volume?

ehild
 
  • #3
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Yes, I believe that is (microfarad); it doesn't say specifically.
I was very unsure on that step and wasn't quite sure how to compute the volume. Do I even to find the volume?
 
  • #4
ehild
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As yo have written, energy density is energy divided by volume. So you need it.

ehild
 
  • #5
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Okay so how do I find the area in order to find volume.
 
  • #6
ehild
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What is the formula for the capacitance?


ehild
 
  • #8
1,540
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The volume between the plates is given by Ad where 'A' is area of the plates and 'd' is separation between them . 'd' is given whereas 'A' is unknown .

Using C= ε0A/d ,find the value of A.

Now,energy density = Energy stored/volume .
 

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