why does a current carrying wire producing magnetic field form closed loops why it is not like electric filed?

Asked by Gaurav Avhad | 23rd Oct, 2010, 02:47: PM

Expert Answer:

Dear student
The direction of a magnetic field line can be revealed using a compass. The magnetic field points away from a magnet near its north pole and towards a magnet near its south pole. Magnetic field lines outside of a magnet point from the north pole to the south. This process works even for situations where there is no magnetic pole. A straight current-carrying wire, for instance, produces a magnetic field that points neither towards nor away from the wire, but encircles it instead.
One important property of the B-field revealed this way is that magnetic B field lines neither start nor end: A generic field line either extends to infinity or wraps around forever without ever rejoining itself exactly to form a closed curve. Special field lines (or all field lines in special magnetic field configurations) form closed curves ("loops"), but they are not generic. (Mathematically, the fact that magnetic field lines never start nor end means that B is a solenoidal vector field.) To date no exception to this rule has been found. (See magnetic monopole below.)

Magnetic field lines exit a magnet near its north pole and enter near its south pole, but inside the magnet B-field lines continue through the magnet from the south pole back to the north.  If a B-field line enters a magnet somewhere it has to leave somewhere else; it is not allowed to have an end point. Magnetic poles, therefore, always come in N and S pairs. Cutting a magnet in half results in two separate magnets each with both a north and a south pole.

A magnetic monopole is a hypothetical particle (or class of particles) that has, as its name suggests, only one magnetic pole (either a north pole or a south pole). In other words, it would possess a "magnetic charge" analogous to an electric charge. Magnetic field lines would start or end on magnetic monopoles, so if they exist, they would give exceptions to the rule that magnetic field lines neither start nor end.

Electric field lines do not form loops because electric field is conservative in nature. Therefore work done by it in a closed loops must be 0. If E lines were to form the Loops, then E.dl, that is the work done by it would have been +ve.

However magnetic force is not conservative in nature. Work done by it in a closed loop is not 0 hence magnetic field lines can form the closed loop.

We hope that clarifes your query.




Answered by  | 25th Oct, 2010, 10:13: AM

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