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

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Homework Help Overview

The discussion revolves around charging a 470µF capacitor to 330V using a 3V battery at a current of 10µA. Participants are exploring the time required for charging, the stored energy in the capacitor, and the current delivered by the battery.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to calculate the charge (Q) using the formula Q = CV and are questioning the correctness of their calculations. There is confusion regarding the appropriate voltage to use for the calculations, as well as the capacitor's value. Some participants express uncertainty about their answers and seek clarification on their methodology.

Discussion Status

There is an ongoing exploration of the problem with participants providing calculations and questioning their accuracy. Some guidance has been offered regarding the need to use the correct values and to confirm the current specified in the problem. Multiple interpretations of the voltage to use in calculations are being discussed.

Contextual Notes

Participants note the potential for errors due to exhaustion and the need for clarity on the capacitor's value and the voltage to be used in calculations. The original problem statement specifies the capacitor's charge voltage as 330V, which is a point of confusion for some.

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

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

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