Physics MCQs for NEET — Practice Questions with Answers

The text states: 'We have partitioned the contribution to the total magnetic field inside the sample into two parts: one, due to external factors such as the current in the solenoid. This is represented by H. The other is due to the specific nature of the magnetic material, namely M. The latter quantity can be influenced by external factors.' (referring to M). H is also due to external factors.

From Eq. (5.15), $B = \mu_0 \mu_r H$. Given $\mu_r = 400$, then $B = \mu_0 (400) H = 400 \mu_0 H$. This is also derived from $\mu = \mu_0 \mu_r$ and $B = \mu H$.

The text explicitly states: 'The three quantities $\chi$, $\mu_r$ and $\mu$ are interrelated and only one of them is independent. Given one, the other two may be easily determined.'

According to the NCERT text, 'Magnetic monopoles do not exist. If you slice a magnet in half, you get two smaller magnets.' Also, 'Unlike electric charges, isolated magnetic north and south poles known as magnetic monopoles do not exist.' This clearly states that magnetic monopoles are not observed in nature.

The NCERT text states: 'Substances, which at room temperature, retain their ferromagnetic property for a long period of time are called permanent magnets.' This differentiates them from other magnetic materials whose magnetic properties are temporary.

According to the NCERT summary: 'When a bar magnet of dipole moment $\vec{m}$ is placed in a uniform magnetic field $\vec{B}$, (a) the force on it is zero, (b) the torque on it is $\vec{m} \times \vec{B}$.' In a uniform magnetic field, the net force on a magnetic dipole (like a bar magnet) is zero, but it experiences a torque aiming to align it with the field.

The NCERT text states: 'The magnetic potential energy $U_m$ is given by $U = -\vec{m} \cdot \vec{B}$, where we choose the zero of energy at the orientation when $\vec{m}$ is perpendicular to $\vec{B}$.'

From the 'POINTS TO PONDER' table under 'Physical quantity Symbol Nature Dimensions Units Remarks', the magnetic moment $\vec{m}$ has dimensions $\text{[L}^{2}\text{A]}$. Its unit is A m$^2$.

The NCERT 'POINTS TO PONDER' states: 'A consequence of the fact that magnetic monopoles do not exist is that the magnetic field lines are continuous and form closed loops. In contrast, the electrostatic lines of force begin on a positive charge and terminate on the negative charge (or fade out at infinity).'

The NCERT text states: 'For diamagnetic materials $\chi$ is negative and small and for paramagnetic materials it is positive and small.' Also, under 'Points to Ponder', it specifies 'For diamagnetic materials $\chi = -10^{-5}$ whereas $\chi = +10^{-5}$ for paramagnetic materials.'