= Magnetizing reactance and reflected resistance in a transformer
{title2=$R_{\mathrm{in}}=(N_p/N_s)^2R_L$}
For an ideal <electrical transformer> with turns ratio $n=N_p/N_s$, the secondary load $R_L$ appears at the primary as $n^2R_L$, while a source resistance $R_g$ appears at the secondary as $R_g/n^2$. A finite magnetizing <inductance> $L_m$ contributes a parallel branch $i\omega L_m$ at the primary; its magnitude must greatly exceed the reflected load for the loaded input to be approximately resistive. The corresponding unloaded secondary self-reactance is $\omega L_m/n^2$. That reactance is distinct from the source's transformed output resistance. A specification that simultaneously calls the loaded input matched to a small resistance and calls the primary impedance very large must distinguish these two branches.
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