Question

A metal wire has a diameter of 0.25mm and
electrical resistivity of metal is 0.8 x 10-8 m.
Find the length of the wire to make a resistance
of 532.
O 30.02m
O
30.26m
30.66m
O 30.72m​

Answer 1

Area of cross-section of the wire, A =? (d/2) 2 Diameter= 0.25 mm = 0.25 x 10^-3 m Resistance, R = 5 ?;rho= 0.8 x 10-8 fi m. We know that R=rho*(l/A) Therefore,l=R*A/rho l=30.66m Therefore,length of the wire = 30.66m If the diameter of the wire is doubled, new diameter=2×0.25=0.5mm=0.5*10^-3m Let new resistance be R1 R1=rho*(l/A’)=rho*(l/? (2d/2) *(2d/2))=R/4 Therefore the resistance becomes 1/4th of the previous R in the given case.

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