Numerical - Nominal fraction for blue light with wavelength given - Metrology & Quality Control

Q.  A surface of 2.1 mm is to be measured using a interferometer. Calculate nominal fraction for blue light which has wavelength of 0.785 μm.
- Published on 07 Aug 15

a. 0.8280
b. 0.5350
c. 0.3185
d. 0.1910

ANSWER: 0.3185

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    Discussion

  • Sravanthi   -Posted on 26 Oct 15
    - Interferometers are used in science and industry to measure changes in refractive index, small displacements and surface irregularities.

    - Principle of superposition is used in interferometers to combine waves.

    Given: Wavelength of blue light = 0.785 μm

    The length of a surface is divided by half wavelength of light to find nominal fraction.

    λ / 2 = 0.785 / 2 = 0.3925 x 10-3 mm

    Number of fringes = 2.1 / 0.3925 x 10-3 = 5350.3184

    Therefore, the nominal fraction for blue light = 0.3184

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