Final answer:
The voltage setting on an x-ray machine controls the penetrating power of the beam, with higher voltage settings resulting in higher energy photons that can penetrate denser materials.
Step-by-step explanation:
The setting on the x-ray machine that controls the penetrating power of the beam is the voltage setting. This setting is responsible for the energy of the x-ray photons, with higher voltages corresponding to higher energy photons and greater penetration. For example, a lower voltage such as 50.0 kV might be used for imaging less dense materials like a chest x-ray, while higher voltages, such as 100 kV, are necessary for looking through denser materials, like a broken leg in a cast. The reason for this is that the density of the material affects how many x-ray photons pass through, with denser materials allowing fewer photons to get through, resulting in a darker shadow on the x-ray image.
Moreover, this high energy of x-rays means they can produce significant ionization in materials, potentially damaging cells in biological organisms. Therefore, modern x-ray usage aims to minimize exposure to the patient and eliminate exposure to others.