Example 9.8: three-lens combinationउदाहरण 9.8: तीन लेंसों का संयोजनExample 9.8: three-lens combination

NCERT Fig 9.20 · Class 12 Physics · Chapter 9 · interactive diagram

Parts and what they mean

• Lens 1: convex, f₁ = +10 cm (लेंस 1: उत्तल, f₁ = +10 cm) — Object at u = −30 cm → 1/v₁ = 1/10 − 1/30 → v₁ = +15 cm.
• Lens 2: concave, f₂ = −10 cm (लेंस 2: अवतल, f₂ = −10 cm) — I₁ is 15 − 5 = 10 cm to its right: a virtual object, u₂ = +10 cm → 1/v₂ = 1/10 + 1/(−10) = 0 → v₂ = ∞ (rays leave parallel).
• Lens 3: convex, f₃ = +30 cm (लेंस 3: उत्तल, f₃ = +30 cm) — Parallel rays focus at its focus: v₃ = +30 cm.
• Principal axis (मुख्य अक्ष) — Line through the optical centre O and the foci.
• A ray through the system (तंत्र से गुज़रती एक किरण) — Bends at each lens; drawn to scale (4 px per cm).
• Towards I₁ (15 cm right of lens 1) (I₁ की ओर (लेंस 1 से 15 cm दाएँ)) — Lens 2 intercepts the rays before they meet.
• Object O (वस्तु O) — 30 cm left of lens 1.
• Final image I (अंतिम प्रतिबिंब I) — 30 cm right of lens 3 (real).
• Object distance 30 cm (वस्तु दूरी 30 cm) — u₁ = −30 cm.
• Separation 5 cm (दूरी 5 cm) — Between lens 1 and lens 2.
• Separation 10 cm (दूरी 10 cm) — Between lens 2 and lens 3 (does not matter here: the light between them is parallel).
• Image distance 30 cm (प्रतिबिंब दूरी 30 cm) — v₃ = +30 cm.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 9.20. Report a mistake