Define polar and non-polar molecules. Explain the behaviour of non-polar molecules in a uniform magnetic field.

An electron falls through a distance of $1.5 \mathrm{cm}$ in a uniform electric field of magnitude $2\times {10}^4 {\mathrm{NC}}^{-1}$. The direction of the field is reversed keeping its magnitude unchanged and a proton falls through the same distance. Compute the time of fall in each case. (Given: $m_e=9.11\times {10}^{-31} \mathrm{kg}, m_p=1.67\times {10}^{-27} \mathrm{kg},$ $q_e=-1.6\times {10}^{-19} \mathrm{C}, q_p=1.6\times {10}^{-19} \mathrm{C}$)

When a $10 \mathrm{\mu C}$ charge is enclosed by a closed surface, the flux passing through the surface is $\varphi$. Now another charge $-5\mathrm{\mu C}$ is placed inside the same closed surface, then the flux passing through the surface is _____.