Capacitors (charging after long time)

[jisbon]

Homework Statement

Find energy stored in capacitor after switch has been closed for long time.

Relevant Equations

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Hi there,
So as far as I know, after long time, current doesn't flow through the resistor That means the voltage drop across the capacitor is equal to the EMF of the cell = 9V
So will the charge be $U = 0.5CV^2$ = $0.5(10)(81)$?
Answer appears to be wrong, not sure what I am doing wrong here.

 

[willem2]

Homework Statement: Find energy stored in capacitor after switch has been closed for long time.

Hi there,
So as far as I know, after long time, current doesn't flow through the resistor .

through what resistor? I think after a long time there won't be any current through the capacitor, and therefore no current through the 3 ohm resistor.

That means the voltage drop across the capacitor is equal to the EMF of the cell = 9V

I can really see no reason for that, no matter which resistor you meant.

If there's no current through the capacitor, you can remove it from the circuit, solve the remaining circuit to find the voltage across the capacitor.

 

[jisbon]

If there's no current through the capacitor, you can remove it from the circuit, solve the remaining circuit to find the voltage across the capacitor.

Won't the voltage across the capacitor be 9v?

 

[sophiecentaur]

Won't the voltage across the capacitor be 9v?

Isn't the 15Ω resistor connected too? Think about its effect.

 

[jisbon]

Ah

Isn't the 15Ω resistor connected too? Think about its effect.

Ah..Solved it :) $1.25x10^{-4}$
Thanks!