1.

A silver wire has a diameter of 0.4 mm and resistivity 1.6×10^-8 ohm metre. How much length of the wire is required to make a 1 ohm coil?

Answer»

Resistance= 1ohm
RESISTIVITY=1.6 * 10-8
DIAMETER=0.4mm
. . . Radius=0.4/2=0.2mm = 0.2/1000 m = 0.2 * 10-3
         (R)2=(0.2 * 10-3)2
        R2=0.04 * 10-6
AREA= PIE * R2=22/7  * 0.04*10-6  
                      = 1.25714286 * 10-6
                       = 1.26 * 10-6 m2
NOW Resistance = resistivity * length / area
              LENGTH= RESISTANCE * AREA / RESISTIVITY
            LENGTH=1 * 1.26 * 10-6 /1.6 * 10-8
                           = 126 * 108 *10/16 * 100 * 106
                          =1260/16
           LENGTH = 78.75 m


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