Calculate time for capacitor to charge and discharge

[Edy56]

Homework Statement

Is the capacitor C= 10μF in the circuit unpolarized or polarized? When the switch is in position (1), the capacitor is charged, and when it is in position (2), the capacitor is discharged. Determine the time required to fully charge the capacitor and the time required to fully discharge the capacitor. It is known: V= 10 V, R1= 15 kΩ, R2= 56 kΩ, R3= 7 kΩ

Relevant Equations

None

I really don't get this one. Why do I need V? Since I didn't use it, I assume my work Is incorrect.

 

[berkeman]

Seems like a trick question; are you sure you copied it exactly? It takes an infinite amount of time to "fully" charge or discharge a capacitor (that's the nature of the exponential funtion).

Also, please learn to use LaTeX to post math equations. There is a link to the "LaTeX Guide" below the Edit window. Thank you kindly.

 

[erobz]

Seems like a trick question; are you sure you copied it exactly? It takes an infinite amount of time to "fully" charge or discharge a capacitor (that's the nature of the exponential funtion).

Also, please learn to use LaTeX to post math equations. There is a link to the "LaTeX Guide" below the Edit window. Thank you kindly.

It looks like they are using the $5\tau$ approximation.

 

[berkeman]

It looks like they are using the $5\tau$ approximation.

Ahh, the old $5\tau$ approximation for $\infty$ -- got it.

 

[DaveE]

You don't need V as long as the criteria for "fully" is a percentage of V, as with the 5τ approximation, which is essentially a 99% done criterion.

 

[Edy56]

You don't need V as long as the criteria for "fully" is a percentage of V, as with the 5τ approximation, which is essentially a 99% done criterion.

Thank you.