Which of the following is used for direct current (DC) applications primarily?

The DC motor is specifically designed to operate with direct current (DC) electricity. In a DC motor, electrical energy is converted into mechanical energy through the interaction of magnetic fields. This is possible because the direction of current flow in the motor windings creates a magnetic field that interacts with a permanent magnet or another magnetic field, causing rotational motion.

In contrast, an alternator generates alternating current (AC), which is not suitable for DC applications. A transformer is used to change the voltage of AC electricity and operates on the principle of electromagnetic induction. It requires AC input and is not applicable for DC systems. Similarly, a step-up transformer increases the voltage of AC but cannot function with DC input. The design and operation of both types of transformers depend on changing magnetic fields, which do not exist in a DC circuit. Therefore, the use of DC motors is essential for applications where direct current is required.