Two independent lamps are incoherent: intensities just add, no fringesदो स्वतंत्र लैंप कला-असंबद्ध हैं: तीव्रताएँ बस जुड़ती हैं, कोई फ्रिंज नहींTwo independent lamps are incoherent: intensities just add, no fringes

NCERT Fig 10.11 · Class 12 Physics · Chapter 10 · interactive diagram

Parts and what they mean

• Two separate sodium lamps (दो अलग सोडियम लैंप) — Light from an ordinary source changes phase abruptly in about 10⁻¹⁰ s, so two lamps never keep a fixed phase relation.
• Opaque screen (अपारदर्शी पर्दा) — Holds the two pinholes.
• Pinholes S₁, S₂ (पिनहोल S₁, S₂) — Each is lit by a different lamp, so S₁ and S₂ are incoherent sources.
• Overlapping light (अतिव्यापी प्रकाश) — The phase difference changes very rapidly, so only the time-average is seen.
• Screen: no fringes (पर्दा: कोई फ्रिंज नहीं) — Average of cos²(φ/2) is ½, so I = 4I₀ × ½ = 2I₀ everywhere — the intensities simply add.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 10.11. Report a mistake