Magnetism and Matter

Sol. $\rho vg-mg=ma$

$\Rightarrow \mathrm{}\frac{\rho vg}{m}=\mathrm{g}+\mathrm{a}$

$\Rightarrow \mathrm{}m=\frac{\rho vg}{g+a}$

$\Rightarrow \mathrm{}\frac{{10}^3\left(\frac{4}{3}\pi *{10}^{-6}\right)\left(9.8\right)}{9.898}$

$\Rightarrow \mathrm{}4.15\mathrm{g}\mathrm{m}$

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer – (b, c, d)

Explanation- If the total magnetic field of the earth is modelled by a point magnetic dipole at the centre, then it is in the same plane of geographical equator, thus the angle of dip at a point on the geographical equator is bounded in a range from positive to negative value.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (a, c, d)

Explanation- Electrostatic shielding is the phenomenon to block the effects of an electric field. The conducting shell can block the effects of an external field on its internal content or the effect of an internal field on the outside environment.

Magnetostatic shielding is done by using an enclosure made of a high permeability

magnetic material to prevent a static magnetic field outside the enclosure from reaching

objects inside it or to confine a magnetic field with in the enclosure.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (a, d)

Explanation- for solenoid H=nI

H= 1000 $*$ 1= 1000 Am

Thus H is a constant, so it is nearly unchanged

B= ${\mu }_0{\mu }_r$ n I

So B $\propto$ ${\mu }_r$

( $\aleph$ )_m)_fero = 10³

( $\aleph$ )_m)_para = 10^-5

$\frac{\left(\right(\aleph \left)\mathrm{m}\right)\mathrm{f}\mathrm{e}\mathrm{r}\mathrm{o}}{\left(\right(\aleph \left)\mathrm{m}\right)\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}}$ = $\frac{{10}^3}{{10}^{-5}}$ = 10⁸

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (a, d)

Explanation- The primary origin of magnetism lies in the fact that the electrons are revolving and spinning of an atom, which gives rise to current called atomic current.

This atomic current gives rise to magnetism. The revolving and spinning about nucleus of

An atom is called intrinsic spin of electron.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer – (a, d)

Explanation – magnetic field lines for magnetic induction B form continuous lines. So lines of B are necessarily continuous across S.

Also H varies inside and outside. So lines of H cannot all be continuous across S

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (b)

Explanation- as curie law explains B $\propto \frac{\mathit{B}\left(\mathit{m}\mathit{a}\mathit{g}\mathit{n}\mathit{e}\mathit{t}\mathit{i}\mathit{c}\mathit{}\mathit{f}\mathit{i}\mathit{e}\mathit{l}\mathit{d}\mathit{}\mathit{i}\mathit{n}\mathit{d}\mathit{u}\mathit{c}\mathit{t}\mathit{i}\mathit{o}\mathit{n}\right)}{\mathit{t}\left(\mathit{t}\mathit{e}\mathit{m}\mathit{p}\mathit{}\mathit{i}\mathit{n}\mathit{}\mathit{k}\mathit{e}\mathit{l}\mathit{v}\mathit{i}\mathit{n}\right)}$

$\frac{I_2}{I_1}=\frac{B_2}{B_1}*\frac{t_1}{t_2}$

_{$I$ 1} =8Am^-1, B₁= 0.6T, t₁=4K

B₂= 0.2T, t₂=16K

So after solving we get I₂= 2/3Am^-

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (b)

Explanation- as gauss's law states $\int E.ds$ = q/ $?$ ₀ for electrostatic field. It does not contradicts for electrostatic fields as the electric field lines do not form continuous closed path

According to gauss's law in magnetic field

$\int E.ds$ =0

It contradicts for magnetic field, because there is a magnetic field inside the solenoid and no field outsid the solenoid carrying current but the magnetic field lines from the closed path.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (d)

Explanation- the individual atoms in a ferromagnetic material possess dipole moment as in a paramagnetic material.

However they interact with one another in such a way that they spontaneously align themselves in a common direction over a microscopic volumes called domain. Thus they align perfectly.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (a)

Explanation- for the earth's magnetism, the magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of earth.

The axis of the dipole not coincide with the axis of rotation of the earth but is presently tilted 11.3⁰ with respect to the later or it is either towards east or towards west