Engineering Calculate time for capacitor to charge and discharge

AI Thread Summary
The discussion centers on the confusion regarding the necessity of voltage (V) in calculating the charging and discharging time of a capacitor. It highlights that while a capacitor theoretically takes an infinite amount of time to fully charge or discharge, the 5τ approximation can be used to estimate when it reaches approximately 99% of its maximum voltage. Participants emphasize the importance of understanding this approximation and suggest using LaTeX for mathematical expressions. Clarification is provided that V is not needed if the criteria for "fully" is based on a percentage of V. The conversation concludes with appreciation for the insights shared.
Edy56
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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
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I really don't get this one. Why do I need V? Since I didn't use it, I assume my work Is incorrect.
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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. :smile:
 
berkeman said:
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. :smile:
It looks like they are using the ##5\tau ## approximation.
 
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erobz said:
It looks like they are using the ##5\tau ## approximation.
Ahh, the old ##5\tau## approximation for ##\infty## -- got it. :wink:
 
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.
 
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DaveE said:
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.
 
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