Charging capacitor: one loop, three surfaces (the puzzle)आवेशित होता संधारित्र: एक लूप, तीन पृष्ठ (पहेली)Charging capacitor: one loop, three surfaces (the puzzle)

NCERT Fig 8.1 · Class 12 Physics · Chapter 8 · interactive diagram

Parts and what they mean

• Conduction current i(t) (चालन धारा i(t)) — Time-varying current in the wires that is charging the capacitor.
• Amperian loop of radius r (त्रिज्या r का ऐम्पियरी लूप) — A circle around the wire; B is the same all along it, so ∮B·dl = B(2πr).
• Point P (बिंदु P) — Point on the loop, outside the capacitor, where we want B.
• Parallel-plate capacitor C (समांतर पट्टिका संधारित्र C) — Being charged; no charge flows across the gap between its plates.
• Flat surface (समतल पृष्ठ) — The wire pierces it, so Ampère’s law gives B(2πr) = μ₀ i.
• Pot-shaped surface (बर्तन जैसा पृष्ठ) — Same rim (the loop) but its bottom lies between the plates: no conduction current crosses it, so the old law would give B = 0. Contradiction!
• Tiffin-box surface (टिफ़िन जैसा पृष्ठ) — A cylinder with a flat bottom S between the plates. No current crosses it either.
• Flat bottom S (between the plates) (चपटी तली S (पट्टिकाओं के बीच)) — What crosses S is the electric field. Its flux Φ_E = Q/ε₀ changes as Q changes.
• Electric field between the plates (पट्टिकाओं के बीच विद्युत क्षेत्र) — Uniform field E = Q/(ε₀A), from the + plate to the − plate, growing while the capacitor charges.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 8.1. Report a mistake