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Concepts Of Physics MCQ Edition [Volume 1]PhysicsDispersion and Spectra

To produce a pure spectrum, the incident light is passed through a narrow slit positioned in the focal plane of an achromatic lens because a narrow slit

Options

  1. Apermits only one colour at a time
  2. Ballows for a more parallel beam upon passing through the lens
  3. Cproduces less diffraction
  4. Dincreases the intensity

Correct answer

B. allows for a more parallel beam upon passing through the lens

Step-by-step solution

A pure spectrum is obtained when there is no overlapping of different colours. If a wide slit is used, it acts as a collection of multiple narrow slits placed side by side. Each narrow slit produces its own spectrum, and these spectra overlap, resulting in an impure spectrum. By using a narrow slit placed at the focal plane of an achromatic lens, the emergent light beam becomes highly parallel. This parallel beam ensures that all rays of a particular wavelength are incident on the prism at the same angle, preventin

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