Answer to Question #133352 in Electricity and Magnetism for ABDUL ALI

Question

describe how iron filings could be used to plot magnetic field pattern around a long straight wire which is carrying a current

Answer 1

The pattern of magnetic field lines around a straight conductor carrying current can be described by the following activity. Insert vertically a long straight wire carrying an electric current so that it passes through the centre of a horizontal piece of plastic board. Take care that the plastic board is fixed and does not move up and down. Now, sprinkle some iron filings onto the plastic board to show the shape of the field. You will notice that the iron filings get arranged round the wires in the shape of circles. This is due to the reason that the magnetic field lines around the current carrying straight conductor are circular.The iron filings align along these field lines. On reversing the direction of flow of current, we observe that the iron filings arrange themselves in circles around the wire showing that the magnetic field lines are still circular in nature. The direction of the magnetic field can be obtained by using a compass. If the current direction is reversed, the direction of the magnetic field is also reversed. When current through the wire is decreased, field also gets reduced. When the current is reversed, field also gets reversed in direction.