How Long to Charge a 470µF Capacitor to 330V with a 3V Battery?

[elips]

A capacitor is used in the electronic flash unit of a camera. A battery with a constant voltage of 3V is used to charge the capacitor to 330V at 10µA. How long does it take to charge the capacitor when C=470µF ? What is the stored energy ? What is the current delivered by the battery?

 

[gneill]

Hi elips, you should show an attempt to solve the problem and indicate where you are getting stuck and need help.

 

[elips]

Well, Q = CV
Q= 10*10^-6*3V
Q=30µC

i = dq/dt
t= 30*10^-6/10*10^-6 Is it true?

Wc= 0.5*C*V^2
Wc= 0.5*10*10^-6*(3^2)
Wc= 4.5 × 10-5µJ Is it true?

I'm not really sure about my answers...

 

[gneill]

Well, Q = CV
Q= 10*10^-6*3V
Q=30µC

I thought that the capacitor was 470µF?

i = dq/dt
t= 30*10^-6/10*10^-6 Is it true?

Well, it's true that a the time required to move a charge Q with a constant current I is

t = Q/I

Wc= 0.5*C*V^2
Wc= 0.5*10*10^-6*(3^2)
Wc= 4.5 × 10-5µJ Is it true?

I'm not really sure about my answers...

You'll want to straighten out your capacitor value in your calculation.

 

[elips]

I thought that the capacitor was 470µF?



Well, it's true that a the time required to move a charge Q with a constant current I is

t = Q/I



You'll want to straighten out your capacitor value in your calculation.

Ohh sorry, I did terrible mistakes, I'm pulling an all nighter which is a pity and I'm aware of this but any way I need to do my homework. So, I guess I'm a bit exhausted as you may notice :/ Can you help me please, sir/madame?

 

[gneill]

Your methodology is okay, you just need to use the correct values.

Capacitor: 470µF charged to 330V at a rate of 10µA

(That's a pretty small current; it'll take a looong time to charge! You might want to confirm this value with the original problem text).

 

[elips]

I thought that the capacitor was 470µF?
Well, it's true that a the time required to move a charge Q with a constant current I is

t = Q/I
You'll want to straighten out your capacitor value in your calculation.

Your methodology is okay, you just need to use the correct values.

Capacitor: 470µF charged to 330V at a rate of 10µA

(That's a pretty small current; it'll take a looong time to charge! You might want to confirm this value with the original problem text).

The thing that confuses me is that I'm not sure which voltage value to use, 3V or 330V..? The rest is easy for me...

 

[gneill]

The problem statement says that the capacitor is charged to 330V.