What is the voltage across a capacitor after a time of two constants when a. charging from zero voltage and b. discharging from a fully charged condition?

Answer 1

U₀ is the max charge of capacitor.

Discharging
U=U₀exp(-t/T)=
=U₀exp(-2T/T)=
=U₀exp(-2)=0.135U₀

Charging
U=U₀{1-exp(-t/T)}=
= U₀{1-exp(-2)}= U₀(1-0.135)=0.865U₀