Magnetic Materials MCQ Questions & Answers in Electrostatics and Magnetism | Physics

Ferromagnetism decreases with rise in temperature. If we heat a ferromagnetic substance, then at a definite temperature, the ferromagnetic property of the substance suddenly disappears and the substance becomes paramagnetic. The temperature above which a ferromagnetic substance becomes paramagnetic is called the Curie temperature of the substance.

It will stay in any position at geomagnetic North and South poles.

A magnetic needle kept in non uniform magnetic field experience a force and torque due to unequal forces acting on poles.

Permeability of soft iron is maximum, so maximum lines of force tries to pass through the soft iron.

$$\eqalign{ & {W_H} = VAft = \frac{m}{d}Aft \cr & = \frac{{0.6}}{{7.8 \times {{10}^3}}} \times 0.722 \times 50 = 277.7 \times {10^{ - 5}}Joule \cr} $$

Iron is a ferromagnetic substance. There are no magnetic lines of force inside a ferromagnetic substance. So, equipment may be protected by placing it inside the can made of a ferromagnetic substance. Hence, it is placed inside an iron can.

For a diamagnetic material, the value of $${\mu _r}$$ is less than one. For any material, the value of $${ \in _r}$$ is always greater than 1.

Paramagnetic material will be feebly attracted, diamagnetic material will be feebly repelled and ferromagnetic material will be strongly attracted.

$$F = \frac{{{\mu _0}}}{{4\pi }}\frac{{{m_1}{m_2}}}{{{r^2}}} = {10^{ - 7}} \times \frac{{30 \times 60}}{{{{\left( {0.3} \right)}^2}}} = 2 \times {10^{ - 3}}N.$$

The moment of inertia of original magnet $$I = \frac{{m{\ell ^2}}}{{12}}$$
After dividing into three equal parts,
$$I' = 3\left( {\frac{m}{3}} \right).\frac{{{{\left( {\frac{\ell }{3}} \right)}^2}}}{{12}} = \frac{I}{9}.$$
Also magnetic moment, $$M' = M$$
Now, $$\frac{{T'}}{T} = \sqrt {\frac{{I'}}{I} \times \frac{M}{{M'}}} $$
$$\therefore T' = T \times \sqrt {\frac{{I'}}{I}} = 2 \times \sqrt {\frac{1}{9}} = \frac{2}{3}s.$$