Which charges make EM waves? (and how the wave sustains itself)कौन-से आवेश EM तरंगें बनाते हैं? (और तरंग स्वयं कैसे चलती रहती है)Which charges make EM waves? (and how the wave sustains itself)

NCERT §8.3.1 · Class 12 Physics · Chapter 8 · interactive diagram

Parts and what they mean

• Charge at rest (विरामावस्था में आवेश) — Produces only an electrostatic field. Nothing changes in time, so no wave.
• Charge in uniform motion (steady current) (एकसमान गति में आवेश (स्थिर धारा)) — Produces a magnetic field too, but it does not vary with time: still no wave.
• Oscillating (accelerated) charge (दोलित (त्वरित) आवेश) — Accelerated charges radiate EM waves. The wave’s frequency equals the frequency of oscillation of the charge.
• Changing electric field (बदलता विद्युत क्षेत्र) — An oscillating E acts like a current (displacement current) and creates B.
• Changing magnetic field (बदलता चुंबकीय क्षेत्र) — An oscillating B induces E (Faraday’s law).
• Ampère–Maxwell law (ऐम्पियर-मैक्सवेल नियम) — Changing E → B: ∮B·dl = μ₀i_c + μ₀ε₀ dΦ_E/dt.
• Faraday’s law (फैराडे नियम) — Changing B → E: ∮E·dl = −dΦ_B/dt.
• The wave moves away at speed c (तरंग चाल c से दूर जाती है) — E and B regenerate each other as the wave travels; its energy comes from the source.

Original diagram drawn by Simple Learning Hub, based on NCERT §8.3.1. Report a mistake