= Solution
For a <Hertzian dipole> of <length> $\ell$ driven at peak <electric current> $I_0$, the <electric dipole moment> <amplitude> is $p_0=I_0\ell/\omega$. Consequently
$$
\overline P=\frac{\omega^4p_0^2}{12\pi\epsilon_0c^3}
=\frac{I_0^2\ell^2\omega^2}{12\pi\epsilon_0c^3}.
$$
The <Hertzian dipole fixed-current power scaling> is thus $\overline P\propto I_0^2\ell^2/\lambda^2$, giving
$$
\boxed{\frac{P_1}{P_2}=\left(\frac{1}{0.5}\right)^2\left(\frac{25}{20}\right)^2=6.25.}
$$
The inverse-fourth-power <wavelength> scaling would hold at fixed <electric dipole moment>, not at the fixed <electric current> specified here.
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