Final answer:
A decrease from 85kVp to 70kVp in an x-ray tube means that the maximum energy of the produced x-rays is reduced, impacting their penetrating power.
Step-by-step explanation:
When the peak voltage (kVp) in an x-ray tube is decreased from 85 kVp to 70 kVp, the maximum energy of the x-rays produced also decreases. This is due to the fact that when an electron is accelerated through a potential given in volts, it acquires energy in electronvolts (eV) that is numerically equal to the accelerating voltage in kilovolts (kV). Therefore, photons produced at a lower potential will have lower maximum energies, affecting their ability to penetrate various materials. This reduction in voltage might be used to tailor the x-ray energies for different types of x-ray imaging procedures or to adjust the dose rate for a patient.