Which of the following changes will increase the heat capacity of an x-ray tube?

Increasing the anode rotation speed in an x-ray tube enhances its heat capacity primarily because it allows for greater heat dissipation. The thermal load produced during x-ray production can be extensive, and rotating the anode spreads this heat over a larger surface area more quickly than a stationary anode. This rapid rotation creates a larger effective target area for the electron interaction, which helps prevent overheating by allowing the heat to dissipate more efficiently into the surrounding materials. Consequently, the heat capacity—the ability of the anode to absorb and manage heat without reaching critical failure temperatures—increases with higher rotation speeds.

The other factors listed do not enhance heat capacity in the same way. Reducing exposure time would decrease the amount of heat generated, while a smaller filament size may limit the x-ray tube's maximum output. A decreased anode angle can also concentrate heat on a smaller surface area, potentially leading to faster overheating rather than improved heat capacity. Thus, the choice of increasing anode rotation speed directly benefits the management of heat within the x-ray tube.