# 5.19 A telephone cable at a place has four long straight horizontal wires carrying a current of 1.0 A in the same direction east to west. The earth’s magnetic field at the place is 0.39 G, and the angle of dip is . The magnetic declination is nearly zero. What are the resultant magnetic fields at points 4.0 cm below the cable?

Number of long straight horizontal wires = 4

The current carried by each wire = 1A

earth’s magnetic field at the place = 0.39 G

the angle of dip = 350

magnetic field due to infinite current-carrying straight wire

r=4cm =0.04 m

magnetic field due to such 4 wires

The horizontal component of the earth's magnetic field

the horizontal component of the earth's magnetic field

At the point below the cable

The resulting field is

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