Final answer:
The true statement is that step-down transformers are designed to decrease the voltage from the primary to the secondary coil, thereby increasing current. This is due to the ratio between the number of turns in their windings being less than one.
Step-by-step explanation:
The statement that transformers which produce a secondary voltage lower than the primary voltage are called step-down transformers is true. A transformer's purpose is to transfer electrical energy between two circuits through electromagnetic induction. The ratio of the secondary to primary voltages in a transformer is determined by the ratio of the number of turns in their windings. Thus, for a step-down transformer, which is designed to decrease voltage while increasing current, this ratio must be less than one. Conversely, a step-up transformer increases voltage and decreases current, and its turns ratio is greater than one. True to their function, step-down transformers often see use in adjusting the high voltages from power lines down to a safer, more usable voltage level in homes and businesses. The power output of a transformer (assuming negligible resistance) is nearly equal to the power input, given by the formula Pp = IpVp = IsVs = Ps, where Pp and Ps represent the primary and secondary power, Ip and Is are the primary and secondary currents, and Vp and Vs are the primary and secondary voltages, respectively.