A step-up transformer with a primary to secondary turns ratio of 1:5 delivers 50 milliamperes to a load. Assuming 100% efficiency, what is the primary current?

In a transformer, assuming 100% efficiency, power is conserved from the primary to the secondary (Power = Voltage x Current). A step-up transformer increases the voltage, but to keep the power constant, it must proportionally decrease the current. With a primary to secondary turns ratio of 1:5, the secondary voltage is 5 times higher than the primary. Consequently, the secondary current is 5 times lower than the primary current. To find the primary current, simply multiply the secondary current (50 mA) by 5, resulting in 250 mA.