KVPY 2020-21 SB SX Exam Previous Papers

Student A : Length of scale = 25 m
Least count = 0.5 cm = 0.005m
Student A can measure the length of 9.5m by using the scale only once so there will be an error of 0.005m in 9.5m
$\therefore$ Relative error $=\frac{0.005}{9.5}=0.0005$
Student B : Length of scale : 1m = 100 cm
Least count = 0.05 cm
To measure 9.5m, student B has to use this meter scale atleast 10 times
$\therefore$ Relative error $=\frac{0.05}{100}\times 10=0.005\mathit{c}\mathit{m}$
Student C : Length of scale : 1 foot = 30.48cm
Least count = 0.05 cm
To measure 9.5m, student C has to use this scale approximately 31 times
$\therefore$ Relative error $=\frac{0.05}{30.48}\times 31=0.05\mathit{c}\mathit{m}$
∴ Relative error is least for Student $\mathit{A}$.