An electron is released from rest near an infinite non-conducting sheet of uniform charge density ' -σ '.The rate of change of de-Broglie wave length…

An electron is released from rest near an infinite non-conducting sheet of uniform charge density ' $\displaystyle -\sigma$ ' .The rate of change of de-Broglie wave length associated with the electron varies inversely as $\displaystyle n^{\text {th }}$ power of time. The numerical value of $\displaystyle n$ is $\displaystyle \_\_\_\_$.