How did the first X-Ray tube work?

The first X-ray tube operated by passing an electrical current through an evacuated tube, which is the foundational principle behind the generation of X-rays. In this tube, electrons were emitted from a heated cathode and then accelerated across the vacuum toward a metal anode. When these high-energy electrons collided with the anode, they produced X-rays. This method allowed for the generation of images based on the differential absorption of X-rays by various tissues in the body, leading to their medical application for diagnostic purposes.

The other options don't accurately describe the functioning of the first X-ray tube. Radioactive material, while related to radiation, was not involved in the fundamental operation of X-ray generation in the early tubes. An electric field plays a role in accelerating electrons but is not the primary mechanism like the electrical current flowing through the tube. Chemical reactions do not generate X-rays in the way that the electrical current does, making this option unrelated to the operation of the first X-ray tube.