Discharging a Capacitor: How Long Does it Take?

[Jimmy25]

Homework Statement

What is the shortest time after which there would be no measurable charge on a 5.0 microfarad capacitor that is charged, then discharged across a 2000 ohm resistance.

a. 0.001 s
b. 0.5 s
c. 10 s
d. 3600 s

Homework Equations

The Attempt at a Solution

According to the time constant the charge on the capacitor should decrease by a factor of 1/e every 0.01 s according to my calculation.

I don't know how to answer the question though.

 

[Gear300]

How much charge is considered unmeasurable?

 

[Jimmy25]

That's my question. How do I answer this without knowing that?