Ch 5Magnetism and Matter — Class 12 Physics, concept-first.

Every bar magnet used in a school laboratory, every compass needle, and the Earth itself are all examples of the same underlying physics: a persistent arrangement of circulating electric charge that p…

The claim. A flat loop of wire carrying a steady current , viewed from a point far away compared to the loop's own size, produces a magnetic field with EXACTLY the same mathematical form as the field…

Section 1.2 showed that ANY current loop carries a magnetic dipole moment. An electron revolving around the nucleus of an atom, in the simple Bohr picture, is exactly such a loop -- a single negative…

Poles cannot be isolated. Every bar magnet has two ends, conventionally called its north (N) pole and south (S) pole, at which the magnetic effect appears strongest.

Consider a short bar magnet of dipole moment , with its S pole at point and N pole at point , a distance apart, centred at .

Now consider a point on the bar magnet's equatorial line -- the perpendicular bisector of the line joining its S and N poles -- at distance from the centre .

No net force, but a net torque. A bar magnet placed in a UNIFORM external magnetic field experiences a force on its N pole (in the direction of ) and an equal and opposite force on its S pole (opposit…

A magnetic field is pictured, exactly like an electric field, using continuous curves called magnetic field lines: the tangent to a line at any point gives the direction of there, and the density of t…

When a material is placed inside a magnetising field, described by the field intensity vector (SI unit ampere/metre, A/m -- distinct from , which includes the material's own response), the material de…

Definition. When a material is magnetised, the enormous number of atomic current loops within it (Section 1.3) become, on average, partially or wholly aligned, so the material as a whole acquires a ne…

Sections 1.9-1.10 described a material's magnetic response in general; this section focuses specifically on FERROMAGNETIC materials, whose response does not vanish the instant the applied field is swi…

Definition. Hysteresis literally means "lagging behind", and it names the characteristic phenomenon, unique to ferromagnetic materials, in which the flux density inside the material always lags behind…

The Earth as a giant bar magnet. A freely suspended magnetic needle anywhere on the Earth's surface settles, after any disturbance, pointing in a fixed direction -- clear evidence that the Earth itsel…

Every material responds, at least a little, to an external magnetic field, and the response falls into one of three sharply distinct classes, characterised by the sign and rough size of the material's…

What an electromagnet is. An electromagnet is a magnet whose field is produced not by permanently aligned atomic dipoles (as in a bar magnet) but by an electric current flowing through a coil, usually…

Sample papers and previous-year board questions for this subject.