On a system with a maximum of 40,000 heat units, which combination of consecutive exposures should not be taken because it would cause overheating of the anode?

On a system with a maximum of 40,000 heat units, which combination of consecutive exposures should not be taken because it would cause overheating of the anode?

• A. Exposure 1 - 40,000 heat units, exposure 2 - 20,000 heat units
• B. Exposure 1 - 20,000 heat units, exposure 2 - 20,000 heat units
• C. Exposure 1 - 25,000 heat units, exposure 2 - 15,000 heat units
• D. Exposure 1 - 10,000 heat units, exposure 2 - 15,000 heat units

Answer: (A)

The key idea is that heat units accumulate in the anode when exposures are consecutive, and you must keep the total below the maximum allowed, otherwise the anode overheats. If the first exposure already uses up the entire 40,000 heat units, there’s no margin left for a second exposure. Adding any additional heat, such as 20,000 heat units, would push the total to 60,000, which exceeds the limit and would cause overheating. The other pairs keep the total at 40,000 or less (20,000 + 20,000 = 40,000; 25,000 + 15,000 = 40,000; 10,000 + 15,000 = 25,000), so they would not exceed the limit even if exposures are consecutive. Therefore, the combination that would cause overheating is the one where the first exposure hits the maximum and a second exposure follows.

The key idea is that heat units accumulate in the anode when exposures are consecutive, and you must keep the total below the maximum allowed, otherwise the anode overheats.

If the first exposure already uses up the entire 40,000 heat units, there’s no margin left for a second exposure. Adding any additional heat, such as 20,000 heat units, would push the total to 60,000, which exceeds the limit and would cause overheating.

The other pairs keep the total at 40,000 or less (20,000 + 20,000 = 40,000; 25,000 + 15,000 = 40,000; 10,000 + 15,000 = 25,000), so they would not exceed the limit even if exposures are consecutive. Therefore, the combination that would cause overheating is the one where the first exposure hits the maximum and a second exposure follows.