Magnetic Effects of Current and Magnetism MCQs for NEET — Physics Questions with Answers

Since the net magnetic flux through any closed surface is zero, any magnetic flux emerging from the North pole (considered positive) must be balanced by an equal amount of magnetic flux entering the South pole (considered negative) within the same closed surface. This is a direct consequence of magnetic field lines forming closed loops.

The NCERT text states: 'Ampere’s law is to Biot-Savart law, what Gauss’s law is to Coulomb’s law. Both, Ampere’s and Gauss’s law relate a physical quantity on the periphery or boundary (magnetic or electric field) to another physical quantity, namely, the source, in the interior (current or charge).' Here, current acts as the source for the magnetic field in Ampere's law, similar to how electric charge acts as the source for the electric field in Gauss's law for electrostatics.

For an electric dipole, the total enclosed charge is $q + (-q) = 0$. According to Gauss's law for electrostatics ($\oint \vec{E} \cdot d\vec{A} = q_{\text{enclosed}}/\epsilon_0$), if the net enclosed charge is zero, the net electric flux through the closed surface is also zero.

The text states: 'These lines called magnetic field lines form closed loops. This is unlike the electrostatic field lines which originate from positive charges and end at negative charges.' This is a key distinction between the two types of fields.

According to the provided text, the total magnetic field B is written as $B = \mu_0 (H + M)$. This equation defines the relationship between these three fundamental magnetic quantities.

The text states that 'where H has the same dimensions as M and is measured in units of A m$^{-1}$'. The table also confirms that both M and H have dimensions [L$^{-1}$ A] and units A m$^{-1}$.

The text explicitly mentions that 'H has the same dimensions as M and is measured in units of A m$^{-1}$'. The summary table also lists 'A m$^{-1}$' as the unit for Magnetic intensity H.

The text defines magnetisation M of a sample to be equal to its net magnetic moment per unit volume: $M = m_{net}/V$ (Eq. 5.7).

The text states that 'χ is small and negative for materials, which are termed diamagnetic. In the latter case M and H are opposite in direction.' Also, 'For diamagnetic materials χ = –10$^{-5}$ whereas χ = +10$^{-5}$ for paramagnetic materials.'

Equation (5.13) in the text explicitly states: $\chi = M/H$, which can be rearranged to $M = \chi H$. This indicates how the magnetization induced in a material is proportional to the applied magnetic intensity.