Question

What is the nature of magnetic field lines of force due to current in a straight wire?

Answer 1

Answer:

They are parallel to each other and doesn't intersect at any point

Answer 2

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When a current is passed through a conducting wire, a magnetic field is produced around it. At a point, the direction of magnetic field will be along the tangent drawn on the magnetic field line at that point. The magneue field lines can be drawn by means of iron filings as follows.

Experiment : Take a sheet of smooth cardboard with a hole at its centre. Place it horizontal and pass a thick copper wire XY vertically through the hole. Connect an ammeter A, battery B, rheostat Rh and a key K between the ends X and Y of the wire. Sprinkle some iron filings on the cardboard and pass an electric current through the wire by inserting the plug in the key K. Gently tap the cardboard.

It is observed that the iron filings get arranged along the concentric circles around the wire. If a small compass needle is placed anywhere on the board near the wire, the direction in which the north pole of needle points, gives the direction of magnetic field at that point which is marked by an arrow on the field line. note that From the magnetic field lines patterns, we

1. The magnetic field lines form the concentric circles around the wire, with their plane perpendicular to the straight wire and with their centres lying on the wire.
2. When the direction of current in the wire is reversed, the pattern of iron filings does not change, but the direction of deflection of the compass needle gets reversed. The north pole of the compass needle now points in a direction opposite to the previous direction showing that direction of magnetic field has reversed.
3. On increasing current in the wire, the magnetic field lines become denser and the iron filings get arranged in circles up to a larger distance from the wire, showing that the magnetic field strength has increased and it is effective up to a larger distance.