Chain 1: Why does the time period of a charged particle in B NOT depend on velocity?

Current-carrying wire creates B (Biot-Savart) → B exerts force on moving charge (Lorentz: F = qvB) → Force is centripetal (⊥ to v) → qvB = $mv^{2}$/r → r = mv/(qB) → period T = circumference/speed = 2πr/v = 2π(mv/qB)/v → v cancels → T = 2πm/(qB) [no v] → Therefore T is velocity-independent. If v doubles → r doubles → circumference doubles → time at same speed doubles → net change: zero. ✓

Chain 2: Why must an ammeter have very low resistance?

Ammeter is placed IN SERIES in a circuit → it carries the same current as the circuit → Ohm's law: V = IR across ammeter → High resistance → large voltage drop → circuit current changes from intended value → inaccurate reading → measurement error → Therefore ammeter must have near-zero resistance to be non-intrusive → Shunt S << G is connected in parallel → most current bypasses galvanometer → R_eff ≈ S ≈ 0.01 $\Omega$.

Chain 3: Why do parallel wires carrying current in the same direction attract each other?

Wire 1 carries current $I_{1}$ upward → creates $B_{1}$ = μ_{0}$I_{1}$/(2πd) at position of wire 2 → $B_{1}$ circles wire 1 (right-hand rule) → at position of wire 2 (to the right of wire 1), $B_{1}$ points into the page → Wire 2 carries current $I_{2}$ upward → Force on wire 2: F = $I_{2}$L × $B_{1}$ → Using F = IL×B with I upward and B into page → F = $I_{2}$L (ĵ) × $B_{1}$(−k̂) = $I_{2}$L$B_{1}$(ĵ × −k̂) = $I_{2}$L$B_{1}$(−î) → Force points toward wire 1 → Attraction. Reverse $I_{2}$ → reverse F direction → Repulsion.

Chain 4: Why do ferromagnets lose magnetism above Curie temperature?

Ferromagnetism arises from quantum exchange interactions → these interactions align neighbouring electron spins → creating macroscopic magnetic domains → thermal energy (k_BT) works against alignment → as T increases → thermal fluctuations increasingly disrupt domain alignment → at Curie temperature T_C: thermal energy ≈ exchange energy → domain structure breaks down → material becomes paramagnetic (random spin orientation) → susceptibility follows Curie-Weiss: χ = C/(T − T_C) for T > T_C.

Chain 5: Why is the magnetic force on a stationary charge zero?

F = qv × B → if v = 0 (charge at rest) → F = q(0) × B = 0 → No force regardless of how strong B is. This is fundamentally different from electric field, where F = qE exists even for v = 0. Electric field acts on CHARGES; magnetic field acts on MOVING charges only.