Diagram 1: Magnetic Field around an Infinite Straight Wire (Cross-section view)

Magnetic Field — Infinite Straight Wire (cross-section) I (out of page) ↑ ↓ → ← $r_{1}$ $r_{2}$ $r_{3}$ B = μ_{0}I / (2πd) — stronger closer to wire d

Diagram 2: Magnetic Field of a Circular Current Loop (side view)

Circular Loop — Magnetic Field Lines → ← B (upward at centre) External field lines R $B_{centre}$ = μ_{0}NI / (2R) [right-hand curl rule]

Key observation: Field lines always form closed loops (no magnetic monopoles). Inside the loop, field lines are straight and dense; outside they curve and spread (weaker). The density of lines represents field strength.