A transformer is an electrical device that generates output voltage depending on the number of turns in its primary and secondary windings. If the turn ratio is greater than one, the transformer is said to be a step-up transformer. It has a higher secondary voltage than the voltage applied at the primary winding. However, if this ratio is less than one, the transformer acts as a step-down transformer, having a lower output voltage than the input. From the energy conservation law, the power delivered at the secondary winding must equal the power generated at the primary winding. By substituting the secondary voltage and rearranging the terms, the expression for the transformation of current is obtained. Expressing the current in terms of resistance and after further simplification, the equation for the primary voltage is obtained. Comparing this equation with Ohm's law gives the transformation equation for resistance. So, a transformer also transforms resistances, along with voltages and currents.