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Finding kilowatt hours from parallel capacitors 
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#1
Mar2410, 03:30 PM

P: 9

1. The problem statement, all variables and given/known data
A parallelconnected bank of 5.00 µF capacitors is used to store electric energy. What does it cost to charge the 2900 capacitors of the bank to 45,000 V, assuming a unit cost of $0.03 per kW·h? 2. Relevant equations CV = Q 1 Joule = 2.77E7 kWh 1 Volt = 1 Joule per Coulomb 3. The attempt at a solution I'm not sure how to convert from Volts to Joules and then to kilowatt hours. I tried CV=Q to find the Coulombs, from where I wanted to find the number of Joules. If my thinking is correct, the 45,000 Volts means there are 45,000 Joules per Coulomb. When i multiplied 5E6 times 45,000 to find Q my result was that the charge was only .225 C for one capacitor, which seems low. I'm not sure where to go from here, and I'm very unsure of how to convert from Volts to Joules to Kilowatt hours. I know at the end I need to remember to multiply my final result by 2900 for the number of capacitors. I also don't know how the fact they're connected by parallel plays into this. Please help! 


#2
Mar2410, 03:40 PM

HW Helper
P: 2,323

Are you familiar with the formula E=1/2CV^2 or E=Q^2/2C? Those are the formulas for the energy stored in a capacitor.



#3
Mar2410, 03:55 PM

P: 9

Okay, i'll try that and see if i can work out the right answer



#4
Mar2410, 04:18 PM

P: 9

Finding kilowatt hours from parallel capacitors
The units for E is in joules correct?



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