CBSE Class 12-science Answered
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.
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