Question

A laser beam has intensity $2.5\times {10}^{14}$ W $m^{-2}$ Find the amplitudes of electric and magnetic fields in the beam.

Answer 1

Given $I=2.5\times {10}^{14}W/m^2$
We know , $I=\frac{1}{2}{ϵ}_0{E}_0^{2}C$
$E_0^2=\frac{2I}{{ϵ}_{0}C}or{E}_0=\sqrt{\frac{2I}{{ϵ}_{0}C}}{E}_0=\sqrt{\frac{2\times 2.5\times {10}^{14}}{8.85\times {10}^{-12}\times 3\times {10}^8}}=0.4339\times {10}^9=4.33\times {10}^{8}N/C{B}_0={\mu }_0{ϵ}_{0}c{E}_0=4\times 3.14\times {10}^{-7}\times 8.85\times {10}^{-12}\times 3\times {10}^8\times 4.33\times {10}^8=1443.\times {10}^{-3}T=1.44T$