Final answer:
An anode with a small angle according to the line-focus principle improves recorded image detail by creating a smaller focal spot, but it does not directly affect heat capacity. The principle is important in the design of X-ray tubes for medical imaging.
Step-by-step explanation:
According to the line-focus principle, an anode with a small angle provides improved recorded detail but not necessarily improved heat capacity. The principle is largely applied in X-ray tubes, where the size of the focal spot affects the sharpness of the image; a smaller focal spot yields greater detail. However, heat capacity is more related to the material and mass of the anode than its angle. An analogy can be drawn with a TV picture tube where a small radius causes electrons to move in tight circles, distorting the image. Similarly, in optics, having the filament at the focal point of a mirror ensures rays emerge parallel rather than focusing energy too intensely, which could be dangerous.