CBSE Class 12-science Answered

Dear Student

Say the crossection of he wire =A

Length of P= L==> Length of Q= 1-L   m

Resistance of initial P=r

After streaching the wire to length 2L resistance of wire R = 4r

==>  resistance of  Q wire = 4r,

Say resistivity of the material = s

resistance of  Q wire = s(1-L)/A=4r   ==>  r=s(1-L)/(4A)------(1)

resistance of  P wire = sL/A=r------------(2)

1,2=====>   s(1-L)/(4A)  =sL/A ==>(1-L)/4=L  ==>  1-L=4L ==>L=1/5=  0.2 m  ;  1-L = 0.8 m

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