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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Light Waves

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Light Waves

In a Young's double slit experiment using monochromatic light of...

In a Young's double slit experiment using monochromatic light of wavelength 620 nm620 \text{ nm}, a transparent paper (refractive index =1.45= 1.45) with a thickness of 0.02 mm0.02 \text{ mm} is pasted over one of the slits. Determine the number of fringes that will cross through the centre upon removal of the paper.

Options

  1. A12.512.5
  2. B14.514.5
  3. C13.513.5
  4. D15.515.5

Correct answer

B. 14.514.5

Step-by-step solution

The path difference introduced by the transparent paper is given by Δx=(μ−1)t\Delta x = (\mu - 1)t.

The number of fringes shifted across the centre upon removal of the paper is n=Δxλ=(μ−1)tλn = \dfrac{\Delta x}{\lambda} = \dfrac{(\mu - 1)t}{\lambda}.

Substituting the given values:

n=(1.45−1)×0.02×10−3620×10−9n = \dfrac{(1.45 - 1) \times 0.02 \times 10^{-3}}{620 \times 10^{-9}}

n=0.45×2×10−56.2×10−7n = \dfrac{0.45 \times 2 \times 10^{-5}}{6.2 \times 10^{-7}}

n=0.9×10−56.2×10−7n = \dfrac{0.9 \times 10^{-5}}{6.2 \times 10^{-7}}

n=906.2≈14.5n = \dfrac{90}{6.2} \approx 14.5

Thus, approximately 14.514.5 fringes will cross through the centre.
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