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JEE Main & Advanced JEE Main Paper (Held On 09-Jan-2019 Evening)

  • question_answer
    In a young's double slit experiment, the slits are placed 0.320 mm apart. Light of wavelength \[\lambda \text{ }=\text{ }500\text{ }nm\] is incident on the slits. The total number of bright fringes that are observed in the angular range \[-30{}^\circ \le \,\theta \le 30{}^\circ \] is: [JEE Main Online Paper (Held On 09-Jan-2019 Evening]

    A) 640                                          

    B) 641

    C) 320                  

    D) 321

    Correct Answer: B

    Solution :

    \[d\,sin\,\theta =n\,\lambda \] \[0.320\,\times \,{{10}^{-3}}.\,\sin 30{}^\circ =n.500\,\,\times \,\,{{10}^{-9}}\] \[n\,\,=\,\,\frac{320\,\,\times \,{{10}^{-6}}}{500\,\times \,{{10}^{-9}}}\,\,\times \,\frac{1}{2}\,\,=\,\,\frac{16}{50}\,\times \,1000\,=\,320\] So, total no. of bright fringes \[=\text{ }2\left( 320 \right)+1=641\]


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