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Magnetism and Matter Class 12 Notes | Magnet and its Properties

Magnetism and Matter Class 12 Notes | Magnet and its Properties :- In the previous article Magnetism and Matter, we read about the discovery of the magnet. In this article we will read about the properties of magnets.

Magnetism and Matter Class 12 Notes – Basic Properties of Magnet

When a bar magnet is hung freely by a thread tied to its center of mass or is floated on still water, then its two ends, called poles, come to rest in the north-south direction. The end which points towards geographical north is called the north pole and the end which points towards geographical south is called the south pole of the magnet.

2. There is mutual repulsion between homogeneous poles of a magnet and mutual attraction between dissimilar poles.

3. The north and south poles of the magnet are slightly inside the geometric ends. The magnetic length (2l) of a magnet is 5/6 times its geometric length (AB).

4. The magnetic poles have the same strength.

5. The north and south poles of a bar magnet cannot be separated. If a bar magnet is divided into two parts, we will get two small separate bar magnets, whose magnetism will be weaker than that of the main bar magnet. Therefore, unlike electric charges, isolated magnetic poles (magnetic monopoles) do not exist.

6. Magnetic materials like iron, nickel, cobalt etc. are attracted by magnets. This force of attraction is maximum at the poles.

7. The force of attraction or repulsion between two magnetic poles is directly proportional to the product of the pole strengths (m₁,m₂) and inversely proportional to the square of the distance (r) between their centers.

$\displaystyle F\propto \frac{{{m}_{1}}{{m}_{2}}}{{{r}^{2}}}$

$\displaystyle \Rightarrow F=\frac{{{\mu }_{0}}}{4\pi }\frac{{{m}_{1}}{{m}_{2}}}{{{r}^{2}}}$ …..(1)

Where μ₀ is the permeability of free space(vacuum).

In CGS system, $\displaystyle \frac{{{\mu }_{0}}}{4\pi }=1$ and

In SI system, $\displaystyle \frac{{{\mu }_{0}}}{4\pi }={{10}^{-7}}wb{{A}^{-1}}{{m}^{-1}}$

SI units of pole strength :-

Let m₁= m₂= m, r = 1 meter and F = 10^-7 N

From equation (1),

$\displaystyle {{10}^{-7}}N=\left( {{10}^{-7}}wb{{A}^{-1}}mtr{{.}^{-1}} \right)\times \frac{m\times m}{{{\left( 1mtr. \right)}^{2}}}$

$\displaystyle \Rightarrow {{m}^{2}}=\frac{Nmtr{{.}^{2}}}{wb{{A}^{-1}}mtr{{.}^{-1}}}$

Now because $\displaystyle 1N=Cmtr.{{s}^{-1}}\frac{wb}{mtr{{.}^{2}}}$ (From F = qvBsinθ)

Therefore

$\displaystyle \Rightarrow {{m}^{2}}=Cmtr.{{s}^{-1}}\frac{wb}{mtr{{.}^{2}}}\frac{mtr{{.}^{2}}}{wb{{A}^{-1}}mtr{{.}^{-1}}}$

$\displaystyle \Rightarrow {{m}^{2}}=C{{s}^{-1}}\frac{mtr.}{{{A}^{-1}}mtr{{.}^{-1}}}$

$\displaystyle \Rightarrow {{m}^{2}}={{A}^{2}}mete{{r}^{2}}$

m = ±1 ampere-meter (Am)

If two identical magnetic poles kept at a distance of 1 m in vacuum (or in air) repel each other with a force of 10^-7 N, then their pole strength will be 1 ampere-meter.

Magnetism and Matter Class 12 Notes | Magnet and its Properties

Magnetism and Matter Class 12 Notes – Basic Properties of Magnet

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