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Calculating capacitance -Got wrong answer

  • Thread starter warnexus
  • Start date
  • #1
90
0

Homework Statement


Find the capacitance of a capacitor that stores 320 MJ(MegaJoules) when the potential difference across its plates is 170V.

Answer must be in nanofarads.

So basically q: is 320MJ
V: is 170V
I need to find C the capacitance.

Homework Equations



To find the capacitance is q=CV.



The Attempt at a Solution



I converted 320MJ to 320* 10 ^ 6 Joules for q. 320* 10 ^6 J is also 320 * 10 ^ 6 Coulombs. Let V the way it is 170V.

Divide (320 * 10 ^ 6 Coulombs) / (170 V) = 1882352.941 Farads. to convert farad to nanofarad I multiply the answer by 10^ 9 and got 1.882352941 * 10 ^ 15 nanofarads.
I put 1.88 * 10 ^ 15 nanofarads but apparently it is the wrong answer.

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
rock.freak667
Homework Helper
6,230
31
In your equation Q=CV, Q is the charge stored.

You are given 320 MJ which is a unit of energy. What is equation for the energy stored by a capacitor?
 
  • #3
90
0
In your equation Q=CV, Q is the charge stored.

You are given 320 MJ which is a unit of energy. What is equation for the energy stored by a capacitor?
that equation would be (1/2)C(V^2). but i do not see your point. i should be using that equation.
 
Last edited:
  • #4
349
1
you know the energy and you know the voltage so using this equation will give you the value of C.
Have you read the question carefully? You have the energy stored as 320 megaJoules.....that sounds totally unreasonable !!! it is about 100kWhr!!!!!
 
  • #5
90
0
Oh! I see. Thanks for the help. Answer is 22 nanofarads.
 

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