Answer:
The pattern of
magnetic field lines around a straight conductor carrying current can be
described by the following activity.
(i) Insert vertically a long straight
wire carrying an electric current so that it passes through the centre of a
horizontal piece of plastic board a shown in figure.
(ii) 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.
(iii) 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.
(iv) 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.
(a) When current through the
wire is decreased, field also gets reduced.
(b) When the current is
reversed, field also gets reversed in direction.
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