Question Analysis: Assertion (A) and Reason (R) based on Moving Coil Galvanometer principles.
Step 1 (Conceptual Analysis of Assertion): [0.5 Mark]
The cylindrical soft iron core serves two purposes:
- It makes the magnetic field radial, ensuring that the plane of the coil is always parallel to the magnetic field lines for any orientation.
- It increases the strength of the magnetic field due to its high magnetic permeability ($\mu_r \gg 1$), which concentrates the magnetic flux lines through the coil.
Step 2 (Conceptual Analysis of Reason): [0.5 Mark]
In a moving coil galvanometer, the radial magnetic field ensures that the plane of the coil is always parallel to the magnetic field lines, not perpendicular. If it were perpendicular, the torque $\vec{\tau} = \vec{m} \times \vec{B}$ would be zero. Thus, Reason (R) is False.
Step 3 (Final Concluded Answer): [1 Mark]
Correct Option: (d) Both Assertion (A) and Reason (R) are false statements.
💡 EL10 Concept Insight: Think of the soft iron core like a magnet-magnet; it doesn't just shape the field lines into a circle, it also acts like a "super-highway" that pulls more magnetic strength into the center, making the galvanometer much more sensitive!