Saturday, 30 April 2016

Magnetic field around a straight conductor carrying current


A  smooth  cardboard  with  iron  filings  spread over  it,  is fixed  in  a horizontal  plane  with  the  help of  a  clamp.
A  straight  wire  passes  through  a  hole made at  the  center
of  the  cardboard.
A current is passed through the  wire  by connecting  its ends to a  battery.
When   the cardboard is gently tapped, it is found that the iron filings  arrange  themselves  along  concentric  circles. This clearly shows that magnetic field is developed around  a  current  carrying  conductor.

To find the direction of the magnetic field, let us  imagine,  a  straight  wire  passes  through  the plane of the paper and perpendicular to it. When a compass needle is placed, it comes to rest in such a way that its axis is always tangential to  a  circular  field  around  the  conductor.
When  the  current  is  inwards the direction of the magnetic field around the conductor looks clockwise.
When the direction of the current is reversed, that it is outwards, the direction of the magnetic pole of the compass needle also changes showing the reversal of the direction of the magnetic field. Now, it is anticlockwise around the conductor. This proves that the direction of the  magnetic  field  also  depends  on  the  direction  of  the  current  in  the conductor. This is given by Maxwell’s rule.