12.1.6. An electromagnetic wave occupies the space between two parallel infinite planes $AB$ and $A'B'$. The illustrated segment of the electromagnetic field moves at the speed of light $c$ in a direction perpendicular to the plane $AB$. The electric field strength of the wave is $E$. By applying the law of electromagnetic induction to the rectangular loop (contour) $baa'b'$, determine the magnetic induction of the wave in SI and CGS units.
Solution
Let $ab=L$.By applying the law of electromagnetic induction to the countour $baa'b'$ we get:
\begin{equation} E L=\frac{d\Phi}{dt} \end{equation}
In time $dt$ the wave moves a distance $cdt$.So the change of the magnetic flux is:
\begin{equation} d\Phi=BLcdt \end{equation}
By plugging eq(2) into the first we find that(in SI units):
\begin{equation} B=\frac{E}{c} \end{equation}
In Gaussian units Faraday's law for the same countour looks like:
