For what situation would you use a step-down transformer?

A step-down transformer is designed to reduce high voltage to a lower voltage, making it suitable for safe use in various applications. This is particularly important in electrical distribution systems, where high voltage from power lines must be transformed to a lower, safer level for residential or commercial use. By stepping down the voltage, the transformer ensures that the electrical devices can operate safely without the risk of damage or electrocution due to excessively high voltage.

In situations where electrical systems operate under high voltage, a step-down transformer allows for the safe transmission and use of electricity. For instance, power plants generate electricity at high voltages for efficient long-distance transmission, and it is only at substations that this voltage is reduced to levels appropriate for homes and businesses.

Other options pertain to different functionalities: converting AC to DC involves rectification, which is not a feature of a step-down transformer; increasing low voltage is the role of a step-up transformer; and providing isolation between circuits typically involves isolation transformers. Thus, the step-down transformer's principal purpose is to safely reduce high voltage for practical usage.