A capacitor is considered to be fully charged after a time period of about how many time constants?

A capacitor is considered to be fully charged after approximately five time constants. The time constant of an RC (resistor-capacitor) circuit, represented by the symbol τ (tau), is defined as the time it takes for the voltage across the capacitor to reach about 63.2% of the maximum voltage when charging.

After one time constant, the capacitor reaches about 63.2% of the final voltage; after two time constants, it reaches about 86.5%; after three time constants, about 95%; and after four time constants, it reaches approximately 98%. By the time five time constants have elapsed, the voltage across the capacitor reaches over 99% of its final value, effectively making it fully charged in practical terms. This understanding is vital for predicting the behavior of capacitors in electronic circuits.

The other options reflect either an incomplete charging period or a misunderstanding of the exponential charging curve of capacitors in RC circuits.