What is the primary purpose of the field coils in a DC motor?

The primary purpose of the field coils in a DC motor is to create a magnetic field that interacts with the armature (rotor) to produce motion. When an electric current is passed through the field coils, a magnetic field is generated, which then interacts with the magnetic field produced by the armature to create a force that causes the rotor to rotate. This rotation is what ultimately drives the motor and allows it to perform its intended function.

Establish a magnetic field