33-15

In strengths of the electric and magnetic fields in an $EM$-wave are always related by the ration

$$E_m=cB_m,$$

so we get the magnetic field value of $6.67\times10^{-9}{\rm T}$.

The intensity is given by the average of the Poynting vector, which is given by

$$\begin{eqnarray*} I &=& S_{avg}\\ &=& \left(\frac{EB}{\mu_0}\right)_{avg}\\ &=... ...c{E_{rms}B_{rms}}{\mu_0}\\ &=& \frac{1}{2}\frac{E_mB_m}{\mu_0}, \end{eqnarray*}$$

which gives the value $5.31\times10^{-3}{\rm W}$.

Finally, since the wave spreads out isotropically, its intensity is everywhere the same on the surface of a sphere. Thus we have

$$I=\frac{P}{A} \to P=4\pi r^2 I,$$

which gives $6.67{\rm W}$.