Transformers have primary and secondary windings, with the primary connected to the power supply and secondary to the load. The turns ratio determines the voltage and current ratios between windings. Total primary resistance is affected by the turns ratio, with secondary resistance referred to primary being R2/k^2 and primary resistance referred to secondary being R1^K^2. No load and short circuit tests are used to measure core and copper losses, with efficiency highest when these losses are equal.