Mathematics in Physics

JEE Main level, single correct, medium

92 of 121

Question 92 of 121

In order to determine the Young's Modulus of a wire of radius 0.2cm0.2cm (measured using a scale of least count =0.001cm=0.001cm) and length 1m1m (measured using a scale of least count =1mm=1mm), a weight of mass 1kg1kg (measured using a scale of least count =1g=1g ) was hanged to get the elongation of 0.5cm0.5cm (measured using a scale of least count 0.001cm0.001cm). What will be the fractional error in the value of Young's Modulus determined by this experiment?

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Answer: (D) 1.41.4%

Y=StressStrain=FLAl=mgLπR2lY=\dfrac{Stress}{Strain}=\dfrac{FL}{Al}=\dfrac{mgL}{\pi {R}^{2}l}
ΔYY=Δmm+ΔLL+2ΔRR+Δll\dfrac{\Delta Y}{Y}=\dfrac{\Delta m}{m}+\dfrac{\Delta L}{L}+2\dfrac{\Delta R}{R}+\dfrac{\Delta l}{l}
ΔYY×100=100[11000+11000+2(0.0010.2)+0.0010.5]\dfrac{\Delta Y}{Y}\times 100=100\left[\dfrac{1}{1000}+\dfrac{1}{1000}+2\left(\dfrac{0.001}{0.2}\right)+\dfrac{0.001}{0.5}\right]
=110+110+1+15=1410=1.4=\dfrac{1}{10}+\dfrac{1}{10}+1+\dfrac{1}{5}=\dfrac{14}{10}=1.4%

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