An electron gun is a device that produces a beam of electrons, which are tiny negatively charged particles. It typically consists of a cathode, which emits electrons when heated, and an anode that accelerates these electrons into a focused beam. Electron guns are commonly used in devices like cathode ray tubes (CRTs) and scanning electron microscopes (SEMs) to create images or perform analyses. In a cathode ray tube, the electron gun directs the beam towards a phosphorescent screen, creating images by illuminating specific areas. In scanning electron microscopes, the electron beam scans the surface of a sample, allowing scientists to observe its structure at a very high resolution.