Q.A magnetic needle kept nonparallel to the magnetic field in a nonuniform magnetic field experiences (A) a force but not a torque (B) a torque but not a force (C) both a force and a torque (D) neither a force nor a torque

[!TLDR] In a nonuniform field the forces on the needle's two poles differ, giving a net force AND a torque -- only a UNIFORM field gi …

Table 12.1's dipole-in-a-field row gives the force on a single pole as $\vec F=q_m\vec B$, exactly analogous to $\vec F=q\vec E$ for a charge. In a UNIFORM field, the forces on a magnet's two poles ($+q_m$ and $-q_m$) are equal in magnitude and exactly opposite in direction, so they always cancel to give zero NET force -- but if the needle is not aligned with the field, these two equal-and-opposite forces act at two different points (the two poles), so they produce a net TORQUE that tends to rotate the needle into alignment, without moving it bodily. In a NONUNIFORM field, however, the field strength (and possibly direction) genuinely differs at the two poles' locations, so the two pole-forces no longer exactly cancel: t …

Apply the force-on-a-pole relation $\vec F=q_mB$ (Table 12.1) to both poles and note that only a UNIFORM field makes the two pole-forces exactly ca …

Assuming a magnetic dipole in ANY external field experiences only a torque -- that is true solely for a UNIFORM field; a nonuniform field ad …