The efficiency of power transformer was depended on the size of copper wire, it meant that the more size of copper wire, the more quantity of current flew and it led to the efficiency of operation, however when changing in the kinds of core from soft core to the corrugated iron core, the result showed that the efficiency of power transformer would be reduced when compared with the same number. As for the usage of old transformer which was smaller and used the electromotive force at 24 volt, the result showed that the secondary coil is smaller, the electromotive force would be smaller also and vise versa and as for the usage of air core, it could not induce to produce the electromotive coil in secondary coil or it could produce but just as little as we could measure, for the rod, it could measure only in the less electromotive force.