Question

Students investigating Weber's law notice that one student is just able to perceive that a black, circular dot on a sheet of paper is larger than another dot when the first dot is 100 mm across and the second is 115 mm across. If the same student is presented with a black, circular dot that is 50 mm across, which of the following is the diameter of a dot that the student would just be able to perceive as being larger?

1) 35 mm
2) 42.5 mm
3) 57.5 mm
4) 65 mm

Answer 1

Applying Weber's law and calculating 15% of 50mm, the diameter of a dot that would be just noticeably larger than the 50mm dot is 57.5mm.

Step-by-step explanation:

The student is asking about an application of Weber's law, which is a principle in psychology related to the just noticeable difference (JND) in stimulus intensity. Specifically, the question deals with the ability to perceive differences in the size of circular dots.

In the given example, the student could detect the difference when the dot was increased by 15mm from 100mm to 115mm, which means the JND for the student is 15%. If we apply this percentage to a smaller dot of 50mm, we need to increase it by 15% to find the smallest size difference that the student can perceive. Mathematically, this is calculated as:

50mm + (15% of 50mm) = 50mm + 7.5mm = 57.5mm.

Therefore, the diameter of a dot that the student would just be able to perceive as being larger than a 50mm dot is 57.5 mm.