If the number density of free electrons in a copper wire is $8.5\times10^{22}cm^{-3}$ and the relaxation time of free electrons in the wire is $2.25\times10^{-14}s$, then the electrical conductivity of copper is (Mass of the electron $=9\times10^{-31}$ kg and charge of the electron $=1.6\times10^{-19}C$)}
Show Hint
Always convert $cm^{-3}$ to $m^{-3}$ before substituting in electrical conductivity problems.