Four point charges, each of $+q,$ are rigidly fixed at the four corners of a square planar soap film of side $\text{'}a\text{'}$. The surface tension of the soap film is $\gamma$. The system of charges and planar film are in equilibrium, and $a=k{\left[\frac{q^2}{\gamma }\right]}^{\frac{1}{N}}$, where $k$ is a constant. Find $N$.

A uniform electric field exists in the region between two oppositely charged plane parallel plates. An electron is released from rest at the surface of the negatively charged plate and strikes the surface of the opposite plate, $2 \mathrm{cm}$ away from the first plate in an interval of $1.5\times {10}^{-8} \mathrm{s}$. The electric intensity is

A uniform electric field exists in the region between two oppositely charged plane parallel plates. An electron is released from rest at the surface of the negatively charged plate and strikes the surface of the opposite plate, $2 \mathrm{cm}$ away from the first plate in an interval of $1.5\times {10}^{-8} \mathrm{s}$. The velocity of the electron when it strikes the second plate is