The simplest modern application of electromagnetism is the probably the DC motor. Using the direct current supplied by a battery, the DC motor turns an electrical coil by passing an electrical current through a wire in a magnetic field. The magnetic field exerts a force on that coil that provides a torque, spinning the coil. This effectively converts the chemical energy in the battery to mechanical energy that can be used, for example, to spin a turbine.
The problem with building a motor like this is that the torque would change directions when the coil reaches its vertical position. If the current runs the same way, but the position of the coil in the magnetic field is different, the direction of the torque would switch. If the direction of the spin changed every 180 degrees, the motor would be useful only as a novelty. The solution to the problem is temporarily breaking the current using a device called a split ring communicator. It’s aligned so that as the coil reaches that troublesome vertical position, the circuit is broken. The coil continues its rotation because of inertia. When the current starts anew the current flows in the opposite direction, and the electromagnet created by the current essentially has reversed poles. It then spins the same way. When it reaches vertical again, the split-ring breaks the current again. By reversing the direction of the current, the motor continues to spin the same direction for the life of the battery. The diagram below represents the coil as an electromagnet. Like colors repel, unlike colors attract. See how the poles switch after the disruption of the current.
Electromagnetism 