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Use a Weber fraction to find the smallest noticeable change

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Psychological, Social, and Biological Foundations

For a participant comparing lifted masses, the Weber fraction, defined as the just-noticeable difference divided by the initial mass, is 0.08. If the initial mass is 250 g250\ \text{g}, what is the smallest increase in mass the participant should detect?

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Answer: C (20 g20\ \text{g})

According to Weber's law, the Weber fraction equals the just-noticeable difference divided by the initial stimulus intensity: k=ΔI/Ik = \Delta I/I. Therefore, ΔI\Delta I =(0.08){}= (0.08)(250 g){}(250\ \text{g}) =20 g{}= 20\ \text{g}. An increase of 2 g2\ \text{g} results from a decimal-place error, and 10 g10\ \text{g} results from unnecessarily dividing the calculated difference by 2. The initial mass of 250 g250\ \text{g} is not the required increase.

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