The electron current is chiefly due to:

Explanation

In an electronic device, such as a vacuum tube or an electron tube, the flow of electrons, also known as electron current, is primarily determined by the cathode. The cathode is a negatively charged electrode that emits electrons through a process called thermionic emission or by other means such as field emission. When a voltage is applied between the cathode and the anode, the cathode releases electrons into the surrounding space, creating a cloud of negatively charged particles. These electrons are then accelerated toward the anode, which is a positively charged electrode. The movement of electrons from the cathode to the anode constitutes the electron current.