A copper wire has diameter 0.5 mm and resistivity of 1.6 � 10��8 Ohm m. What will be the length of this wire to make its resistance 10 Ohm? How much does the resistance change if the diameter is doubled?

Area of cross-section of the wire, A =pi (d/2) 2 Diameter= 0.5 mm = 0.0005 m Resistance, R = 10Ohm We know that length of the wire = 122.72 m If the diameter of the wire is doubled, new diameter = 2 0.5 = 1mm = 0.001 m Let new resistance be R Therefore, the length of the wire is 122.7 m and the new resistance is 2.5 Ohm.

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