Physics · Magnetism And Matter · NEET
Only outside the magnet. Outside, lines run from North to South, so it looks like they start at N. But inside the magnet they run from South to North, joining up to make one closed loop. So a field line has no true starting point or ending point — it is a continuous closed loop. This is the biggest difference from electric field lines, which do start on +q and end on -q.
The tangent to a field line gives the direction of the net field B at that point. If two lines crossed, there would be two different tangents, meaning two directions of B at the same point. A field cannot point in two directions at once, so lines never intersect.
No — this is a common trap. NCERT warns that unlike electric field lines, magnetic field lines do NOT give the direction of force on a moving charge. The force is F = qv × B, which is perpendicular to both v and B. The line only gives the direction of B itself (via the tangent).
The number of lines crossing per unit area tells you the magnitude of B. Where lines are crowded (near the poles), B is strong; where they spread out, B is weak. It is the relative density that matters, not the absolute count.
No. They are a visual tool to picture the field. Iron filings line up along them, but the field itself is continuous everywhere. How many lines you draw is your choice — only their direction and relative spacing carry physical meaning.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
(1) They form continuous closed loops with no break. (2) The tangent at any point gives the direction of net field B. (3) They never cross each other. (4) Density of lines shows the strength of B — denser means stronger. (5) Outside a magnet they go N to S; inside they go S to N.
Because magnetic monopoles do not exist. A field line cannot start or stop at an isolated pole, so it must close on itself. This is expressed by Gauss's law for magnetism: the net magnetic flux through any closed surface is zero.
Magnetic lines are closed loops and never start or end; electric lines start on +q and end on -q (open curves). Also, magnetic lines do NOT give the force direction on a moving charge, while electric lines do give force direction on a charge.
At the poles, where the field lines are most crowded together. The field is weakest at points far from the magnet, where the lines spread far apart.
Yes. Magnetic field line properties are directly asked as statement/assertion questions and connect to Gauss's law for magnetism, bar magnet vs solenoid, and the comparison with electric field lines — all high-yield in Magnetism and Matter.
