How Is Energy Calculated in a Charged Capacitor?

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Homework Statement

1) A 4.7-mu or micro FF capacitor is charged to 290 V. How much energy is stored in the capacitor?

2) How much additional energy is required to charge the capacitor from 290 V to 780 V?

Homework Equations

U = 1.2*C*V²

The Attempt at a Solution

The first one I got right...

1) U = 1/2*(4.7 * 10^-6)*290 = 1.975E-1

2) I thought to find this one you could use the change in energy would have to equal the change in potential? So I tried this...but its not right, can anyone tell me where I went wrong? thanks!

Uf - 1.975E-1 = .5*(4.7E-6)(780)² - .5*4.7E-6*290²

Uf = 1.4297 J

 

[cse63146]

I did Uf - 1.975E-1 = .5*(4.7E-6)(780)2 - .5*4.7E-6*290^2

but I got 1.232