Dispersion — Achromatic DoubletMediumQuestion 20256
Question
An achromatic doublet (convex lens of one glass + concave of another) corrects chromatic aberration by:
- AMaking all colours have the same focal length by combining two glasses with matched dispersive powersCorrect
- BBlocking certain wavelengths
- CUsing only one colour of glass
- DIncreasing aperture
Correct answer
Making all colours have the same focal length by combining two glasses with matched dispersive powers
Explanation
Condition for achromatic doublet: ω₁/f₁ + ω₂/f₂ = 0 where ω is dispersive power. The two glasses have different dispersive powers — the doublet corrects dispersion while maintaining net converging power. Used in cameras, telescopes, and eyepieces.