Final answer:
The psychophysicist is investigating the difference threshold, specifically through Weber's Law, which relates to the just noticeable difference in stimuli being proportional to the original stimulus.
Step-by-step explanation:
The psychophysicist in this scenario is investigating the difference threshold, also known as the just noticeable difference (jnd). This concept relates to how much difference in stimuli is required to detect a difference between them. The difference threshold is the minimum difference between two stimuli that a person can detect 50% of the time. When the psychophysicist asks the subject to compare a 10-pound weight to a weight that is 10 pounds and 2 ounces, they are testing to see if the subject can perceive the slight increase in weight, which relates directly to Weber's Law.
Weber's Law suggests that the just noticeable difference between two stimuli is proportional to the magnitude of the original stimulus. Therefore, as the weight increases, the additional weight required for a difference to be noticeable also increases. Since the test involves detecting a small difference in weight relative to a baseline weight, and this aligns with the principles of Weber's Law, the correct answer to the student's question is A) Weber's Law.