1.the resistiviy of micron wire 100micro ×ohm×cm . what length of wire of diameter 0.2mm is required to form a coil of resistance 20 ohm 2. If its streched to triple to its length what will be its resistance then
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Wire A.
Length = l.
Radius =r.
Area =pie r2.
R1= rho x l /pie r2.
Wire B.
Length = 2l.
Radius = 2r.
Area = pie 4r2.
R2= rho x 2l/pie 4r2=rho x l /pie x 2r2.
total resistance.
1/Rp= 1/R1+1/R2.= pie r2/rho x l+2 pie r2/ rho x l.=3 pie r2/rho x l.
Rp= rho x l/ 3 pie x r2.
ratio = Rp/ R1= rho /3 pie r2divided by rho x l / pie x r2.
Rp / R1= 1 : 3.
Hope it helps you
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