Explanation: A series DC motor's field winding is connected in series with its armature. This means the armature current also provides the motor's magnetic field (flux). When the mechanical load is removed, the motor will naturally try to speed up. As speed increases, the back electromotive force (EMF) generated by the armature increases. This increased back EMF reduces the armature current. Critically, because the field flux is produced by the armature current, a reduced current also means a reduced magnetic field. Since back EMF is proportional to (flux × speed), a weaker field requires an even higher speed to generate the necessary back EMF to counteract the supply voltage. This creates a runaway effect: less load leads to higher speed, which reduces current and flux, which then requires even greater speed to maintain the back EMF. This feedback loop causes the motor to accelerate uncontrollably until it mechanically fails.