In an x-ray tube, which two components are essential to form the cathode?

The cathode in an x-ray tube consists of two critical components: the filament and the focusing cup.

The filament is responsible for emitting electrons when heated; it acts as the source of electrons needed for the x-ray generation. When an electric current passes through the filament, it heats up and produces a cloud of electrons around it due to thermionic emission.

The focusing cup is designed to help direct the emitted electrons towards the anode. It has a negatively charged metal structure that surrounds the filament, helping to focus the electron stream into a more concentrated beam. This focusing is vital because it increases the efficiency of x-ray production by ensuring that more electrons collide with the anode target, where they produce x-rays.

In contrast, the other choices refer to components that do not comprise the cathode. The target is part of the anode, and the grid serves a different function in x-ray tubes, such as reducing scatter radiation. Recognizing the specific roles and components of the x-ray tube is essential for understanding the overall operation of radiographic testing.