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JEE Main 2020 (5 Sep, Shift 1) · Errors in Measurement

Errors in Measurement question from JEE Main 2020 (5 Sep, Shift 1)

Q91JEE Main 2020 · 5 SEP · SHIFT 1Medium

Errors in Measurement

A physical quantity z depends on four observables

a, b, c and d, as z = a2b23c d3\frac{a^{2} b^{\frac{2}{3}}}{\sqrt{c}\, d^{3}}. The percentages of error in the measurement of a, b, c and d are 2%, 1.5%, 4% and 2.5% respectively. The percentage of error in z is:

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Answer: (b)

  1. z=a2b2/3c d3⇒Δzz=2Δaa+23Δbb+12Δcc+3Δddz = \frac{a^2 b^{2/3}}{\sqrt{c}\, d^3} \Rightarrow \frac{\Delta z}{z} = 2\frac{\Delta a}{a} + \frac{2}{3}\frac{\Delta b}{b} + \frac{1}{2}\frac{\Delta c}{c} + 3\frac{\Delta d}{d}
  2. =2(2)+23(1.5)+12(4)+3(2.5)=4+1+2+7.5=14.5%= 2(2) + \frac{2}{3}(1.5) + \frac{1}{2}(4) + 3(2.5) = 4 + 1 + 2 + 7.5 = 14.5\%
  3. So the answer is (b) 14.5%14.5\%.
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