  We study rolling radion dynamics of electrified D-brane in NS5-brane
background, both in effective field theory and in full open string theory. We
construct exact boundary states and, from them, extract conserved Noether
currents. We argue that T-duality and Lorentz boost offer an intuitive
approach. In the limit of large number of NS5-branes, both boundary wave
functions and conserved currents are sharply peaked and agree with those
deduced from the effective field theory. As the number of NS5-branes is
reduced, width around the peak becomes wider by string corrections. We also
study radiative decay process. By applying Lorentz covariance, we show how the
decay of electrified D-brane is related to that of bare D-brane. We compute
spectral moments of final state energy and winding quantum number. Using
Lorentz covariance argument, we explain in elementary way why winding quantum
number should be included and derive rules how to do so. We conclude that
Kutasov's "geometric realization" between radion rolling dynamics and tachyon
rolling dynamics holds universally, both for bare and electrified D-branes.
