Visual Summary — Diagrams and Comparison Tables — Summary

Solenoid vs Toroid Cross-Section (Side View)

Solenoid vs Toroid — Field Comparison

SOLENOID

B = μ_{0}nI (uniform) B ≈ 0 outside N S

TOROID

B=0 (hollow) B = μ_{0}NI/(2πr) in ring B = 0 outside r

Key Difference: Solenoid has open ends; Toroid is closed — field fully confined

Magnetic Materials Comparison (Quick Reference)

	Diamagnetic	Paramagnetic	Ferromagnetic
χ	< 0	0 < χ << 1	>> 1
μᵣ	< 1	~1	>> 1
Examples	Cu, Bi, $H_{2}O$	Al, $O_{2}$ , Pt	Fe, Co, Ni
In field	Repelled	Weakly attracted	Strongly attracted
Temperature	Independent	χ = C/T	Hysteresis; Curie temp

Galvanometer Conversion Summary

Galvanometer Conversions AMMETER Shunt S in PARALLEL G S (small) S = IᵍG/(I − Iᵍ) R_eff = GS/(G+S) ≈ S VOLTMETER Series R in SERIES R (big) G R = V/Iᵍ − G R_eff = G + R ≈ R (Very high resistance)