Physics Ncert Solutions Class 12th

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(a, b, d) A metal plate is getting heated when a DC or AC current is passed through the plate, known as heating effect of current. Also, when metal plate is subjected to time varying magnetic field, the magnetic flux linked with the plate changes and eddy currents comes into existence which make the plate hot.

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(b) The self-inductance of a long solenoid of cross-sectional area A and length l, having n turns per unit length, filled the inside of the solenoid with a material of relative

permeability (e g. ., soft iron, which has a high value of relative permeability) is given by the relation L = ${\mu }_r{\mu }_o$ n²A/l

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(a) When the current in B (at t= 0) is counter-clockwise and the coil A is considered above to it. The counterclockwise flow of the current in B is equivalent to north pole of magnet and magnetic field lines are emanating upward to coil A. When coil A start rotating at (t= 0), the current in A is constant along clockwise direction by Lenz's rule.

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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.

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(b) When the A stops moving the current in B become zero, it is possible only if the current in A is constant. If the current in A would be variable, there must be an induced emf (current) in B even if the A stops moving.

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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.

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(b) When cylindrical bar magnet is rotated about its axis, no change in flux linked with the circuit takes place, consequently no emf induces and hence, no current flows through the ammeter A.

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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

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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.

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$\varnothing =B.A$

And A= A₁+A₂= (L²k+L²i)

B= B_o (i+k)T

$\varnothing =B.A$= B_o (i+k) (L²k+L²i)

= 2B_oL²Wb