Final answer:
When the enclosure has only a little gas, electrons travel more freely from the cathode to the anode, resulting in fewer x-rays and more heat production due to less resistance affecting the electron flow.
Step-by-step explanation:
When just a little gas is in the enclosure, the electron flow from cathode to anode is unimpeded, fewer x-rays are produced, and the more heat is generated. As electrons are ejected from the cathode and accelerated towards the anode in a cathode ray tube (CRT), they collide with the material of the anode, ionizing atoms and causing some electrons within the anode material to move to higher energy states. When these electrons return to their original energy levels, they emit x-rays. The production of x-rays happens when electrons decelerate or when they fill a vacancy in the inner shell of an atom, causing the emission of characteristic x-rays. However, if there is less gas in the enclosure, there is less resistance against the electron flow, leading to more efficient conversion of their kinetic energy primarily into heat instead of x-ray production.