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JEE Main 2021 (25 Jul, Shift 1) · YDSE: Fringe Width & Fringe Positions

YDSE: Fringe Width & Fringe Positions question from JEE Main 2021 (25 Jul, Shift 1)

Q57JEE Main 2021 · 25 JUL · SHIFT 1Medium

YDSE: Fringe Width & Fringe Positions

In the Young's double slit experiment, the distance between the slits varies in time as d(t) = d0 + a0 sinω\omegat; where d0, ω\omega and a0 are constants. The difference between the largest fringe width and the smallest fringe width obtained over time is given as:

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Answer: (b)

  1. β=λDd\beta = \frac{\lambda D}{d}; dd ranges from d0−a0d_0 - a_0 to d0+a0d_0 + a_0
  2. βmax=λDd0−a0\beta_{max} = \frac{\lambda D}{d_0 - a_0}, βmin=λDd0+a0\beta_{min} = \frac{\lambda D}{d_0 + a_0}
  3. βmax−βmin=λD(d0+a0)−(d0−a0)d02−a02=2λDa0d02−a02\beta_{max} - \beta_{min} = \lambda D \frac{(d_0 + a_0) - (d_0 - a_0)}{d_0^2 - a_0^2} = \frac{2\lambda D a_0}{d_0^2 - a_0^2}
  4. So the answer is (b).
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