During exposure, what is the charge on the focusing cup in the x-ray tube?

The charge on the focusing cup in the x-ray tube is negative during exposure. This negative charge serves a crucial function within the x-ray tube's operation. The focusing cup helps to direct and focus the stream of electrons emitted from the cathode towards the anode.

When the filament in the cathode is heated, it releases electrons through a process called thermionic emission. The negative charge of the focusing cup repels these electrons, effectively guiding them into a narrow beam aimed at the anode. This focused stream is essential for the efficient production of x-rays, as it ensures that the electrons hit the anode in a concentrated area, facilitating the conversion of kinetic energy from the electrons into x-ray photons.

Understanding the role of the focusing cup and its negative charge is vital for grasping the operating principles of x-ray tubes, especially in the context of how electron movement is manipulated to create medical imaging.