A2.0 µf capacitor is charged through a 50,000 ohm resistor. how long does it take for the capacitor to reach 90% of full charge?

0.23 s

Explanation:

First of all, let's find the time constant of the circuit:

where

is the resistance

is the capacitance

Substituting,

The charge on a charging capacitor is given by

(1)

where

is the full charge

we want to find the time t at which the capacitor reaches 90% of the full charge, so the time t at which

Substituting this into eq.(1) we find

answer: a. same unit

explanation: