A continuous spectrum is produced by Bremsstrahlung, the electromagnetic radiation produced when free electrons are accelerated during collisions with ions. A line spectrum results when an electron having sufficient energy collides with a heavy atom, and an electron in an inner energy level is ejected from the atom. An electron from an outer energy level then fills the vacant inner energy level, resulting in emission of an X-ray photon. For example if an electron in the n = 1 energy level is ejected from an atom, an electron in the n = 2 level of the atom can fill the vacancy created in the n = 1 level, and a photon with an energy equal to the energy difference between the two levels will be emitted. A scientist produced both types of spectra using the X-ray tube shown in the Fig.1. The tube contains a heated filament cathode (C), which emits electrons. A power supply (LV) regulates the filament temperature, the electrical current in the tube, and the number of X-rays produced at the anode (A). Another power supply (HV) regulates electron acceleration. The scientist used an X-ray tube to determine the relationship between X-ray wavelength, $\mathrm{\lambda }$ and X-ray intensity I, which is proportional to the number of X-ray photons emitted at $\mathrm{\lambda }$. The scientist then graphed the results of the experiment, as shown in Fig. 2.