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Dispersion and Spectra — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsDispersion and Spectra1 Mark
MCQ
Which of the following quantities increase when wavelength is increased? Consider only the magnitudes.
  1. The power of a converging lens.
  2. The focal length of a converging lens.
  3. The power of a diverging lens.
  4. The focal length of a diverging lens.
  • A
    Only $A$
  • B
    $A$ and $B$
  • ✓
    $B$ and $D$
  • D
    $C$ and $D$
✓

Answer

Correct option: C.
$B$ and $D$
The focal length of a lens is inversely proportional to the refractive index of the lens and the refractive index of the lens is inversely proportional to the square of wavelength. Therefore, the focal length is directly dependent on wavelength; it increases when the wavelength is increased.

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