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MHT CET 2025 (20 Apr, Shift 2) · Prism, Dispersion & Scattering

Prism, Dispersion & Scattering question from MHT CET 2025 (20 Apr, Shift 2)

Q26MHT CET 2025 · 20 APR · SHIFT 2Medium

Prism, Dispersion & Scattering

An achromatic convergent doublet of two lenses in contact has a power +2 D. The convex lens has power +5 D. The ratio of the dispersive powers of the convergent and divergent lenses is (in magnitude)

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Answer: (a)

  1. P=P1+P2⇒2=5+P2⇒P2=−3 DP = P_1 + P_2 \Rightarrow 2 = 5 + P_2 \Rightarrow P_2 = -3\,D.
  2. Achromatism: ω1P1+ω2P2=0⇒∣ω1ω2∣=∣P2P1∣=35\omega_1 P_1 + \omega_2 P_2 = 0 \Rightarrow \left|\dfrac{\omega_1}{\omega_2}\right| = \left|\dfrac{P_2}{P_1}\right| = \dfrac{3}{5}.
  3. So the answer is (a) 3:53 : 5.
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