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A copper wire of cross sectional asrea 0.01 cm is under a tension of 20 N. Find the decrease in the cross sectional area. Young modulus of copper `=1.1xx10^11Nm^-2` and Poisson ratio 0.32.

Answer» Correct Answer - A::B::C::D
`A=0.01 cm^2`
`=10^-6m^2`
`=T=20N`
`Y=1.1xx10^11N/m^2`
we know that `Y=(FL)/(A/_\\L)`
`=(/_\\L)/L=F/(AY)`
`=20/(10^-6xx1.1x10^11)x18.18xx10^-5`
`d=((/_\\D)/D)/((/_\\L)/L)=0.32`
`So, (/_\\D)/D=(0.32)xx(KL)/L`
`=32xx(18.18)xx10^5=5.81xx10^-5`
Again `(/_\A)/A=(2/_\\r)/r`
`rarr /_\\A=(2/_\\r)/r`
`/_\\A=2xx(5.8xx10^-5)xx(0.01)`
`=1.16xx10^9N/m^2`


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