3. A long straight wire in the horizontal plane carries a current of 50 A in north to south direction. Give the magnitude and direction of B at a point 2.5 m east of the wire.
The magnitude of the magnetic field at a distance r from a long straight wire carrying current I is given by,
In this case
(current=50A, distance= 2.5m, permeability of free space = 410-7 TmA-1)
The current is going from the North to South direction in the horizontal plane and the point lies to the East of the wire. Applying Maxwell's right-hand thumb rule we can see that the direction of the magnetic field will be vertically upwards.