= Solution
The <intensity of an isotropic radiator> at distance $r$ is the radiated <power> divided by spherical area: $\mathcal I=P/(4\pi r^2)$. For a locally plane far-field <electromagnetic wave> in air, its mean <Poynting flux> is $\mathcal I=E_{\mathrm{rms}}^2/Z_0=E_{\mathrm{peak}}^2/(2Z_0)$, where the vacuum <wave impedance> is $Z_0\simeq376.7\ \Omega$. Thus
$$
\mathcal I=\frac{10^5}{4\pi(10^5)^2}\simeq7.96\times10^{-7}\ \mathrm{W\,m^{-2}},
$$
and
$$
\boxed{E_{\mathrm{rms}}\simeq1.73\times10^{-2}\ \mathrm{V\,m^{-1}},\qquad E_{\mathrm{peak}}\simeq2.45\times10^{-2}\ \mathrm{V\,m^{-1}}.}
$$
Both conventions are given because “field strength” alone does not specify RMS or peak. This estimate treats the stated transmitter <power> as radiated power and ignores ground reflection and absorption.
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