Answer
$
\text { Since the current } i \text { is a periodic function of }\\ t \text { with period } T \text {, so must be } U_B \text {. }
$
Work Step by Step
$
\text { Since the current } i \text { is a periodic function of }\\ t \text { with period } T \text {, so must be } U_B \text {. }
$
