Weber's law: calculating the just-noticeable difference
A person can just detect the difference between a 100 g weight and a 102 g weight. According to Weber's law, what is the smallest detectable increase from a 500 g weight?
Answer C: explanation for every choice
A
This treats the just-noticeable difference as a fixed amount. Weber's law says it is a fixed proportion.
B
This uses a 1% ratio instead of 2%.
C
Correct. The Weber fraction is 2/100 = 0.02, and 0.02 × 500 g = 10 g.
D
This doubles the ratio to 4%.
TakeawayThe just-noticeable difference is a constant fraction of the starting stimulus, not a constant amount.
Equation usedWeber's law
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