The voltage equation for a DC motor is expressed as:
\[
V = Eb + Ia Ra
\]
In this equation:
V represents the applied voltage to the armature.
Eb is the back electromotive force (emf), generated as the motor rotates.
Ia denotes the armature current, which is the flow of current through the motor's armature winding.
Ra signifies the resistance of the armature winding.
The armature current (Ia) is significant as it directly impacts the motor's torque output. The voltage equation establishes equilibrium between the applied voltage, the back emf, and the voltage drop across the armature resistance caused by Ia.