Final answer:
In a typical electron gun, a potential difference between metal plates accelerates electrons to an energy level measured in electron volts, equivalent to the voltage applied. For example, a 5000 V potential difference produces 5000 eV electrons. This concept is universally applicable, such as in X-ray tubes, with adjustable voltages for varying energies of X-rays.
Step-by-step explanation:
A typical electron gun accelerates electrons by using a potential difference between two metal plates. When an electron is accelerated through this potential difference, its kinetic energy will be equivalent to the energy given by the voltage in electron volts (eV). Hence, the energy of the electron in eV is numerically equal to the voltage across the plates. For example, if a 5000 V potential difference is applied, it produces 5000 eV electrons. This principle applies universally, so if a potential difference of, say, 50.0 kV is used, it generates 50.0 keV electrons which can produce photons with a maximum energy of 50 keV.
In the context of the question, the potential difference between the photocathode and anode in a tube that such an electron gun might be a part of, ensures that electrons produced by photoemission are sufficiently accelerated towards the anode. Various devices, including X-ray tubes, often have adjustable potential differences to allow for the creation of different energy levels for electrons which in turn affects the penetrating ability of resultant X-rays.