Consider the $R L$ circuit of Fig. 32-6. In terms of the battery emf $\mathscr{E}$, (a) what is the self-induced emf $\Delta V_{2}$ when the switch has just been closed on $a$, and (b) what is $\Delta V_{2}$ when $t=2.0 \tau_{L} ?$ (c) In terms of $\tau_{L}$, when will $\Delta V_{2}$ be just one-half the battery emf $\mathscr{E}$ ?