DC motor:
motor effect
The primary purpose of this is to convert electrical energy into kinetic energy. The main why this operates is through the motor effect, which is a phenomenon where when a current in a conductive material is exposed to an external magnetic field travelling perpendicular to the current's direction, a force is exerted perpendicular to the current and the mag field. this is used in the dc motor as when a current is passed through the coil, the magnetic field produces a force on the coil.
torque and split ring
Since both sides of the coil perpendicular to the mag field are travelling in opposite directions, the force applied in opposite directions, which produces a torque on the coil which makes it a spin. if the coil were to continue spinning, the direction of the forces would actually remain the same direction, so there would be a point where the angular velocity is opposite to the direction of the torque which slows down the motors speed. So a mechanism called a split-ring commutator is required to switch the current every half turn so the direction of both quantities remain the same and the motor keeps spinning. This commutator is connected to rotating carbon brushes connected to a power supply.
back emf
as the motor spins, the crossectional area is exposed to a magnetic flux that constantly changes, which induces an emf or voltage across the coil, hence generating a current the opposite direction of the supplied voltage. despite the perceived loss of energy, the back emf is actually an integral part of the motor. it's very hard to get rid of as it's inherent within the movement, and it also moderates the current to a manageable level for the coil. without back emf, the coil would actually overheat with the supplied current. this is observed if you somehow stop the rotation of the coil, you will most likely see this happen, e.g. drill is stuck in ground --> stop rotating --> overheats
DC generator:
is the same as the dc motor but opposite. instead, it converts kinetic/mechanical energy whatever you want to call it into electrical using back emf as the principle to generate a current and produce electricity. split ring commutator is required to keep it dc (one direction), otherwise it would be an ac current produced
