Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2009

  • question_answer
    The spacing between the principal planes of a crystal is \[4\,\overset{\text{o}}{\mathop{\text{A}}}\,\]. It is found that first order bragg reflection of a beam of monochromatic X-rays occurs at an angle of \[30{}^\circ \]. The wavelength of X-rays is

    A) \[4\,\overset{\text{o}}{\mathop{\text{A}}}\,\]

    B) \[2\,\overset{\text{o}}{\mathop{\text{A}}}\,\]

    C) \[1\,\overset{\text{o}}{\mathop{\text{A}}}\,\]

    D) \[1.5\,\overset{\text{o}}{\mathop{\text{A}}}\,\]

    Correct Answer: A

    Solution :

    Using the Bragg's formula \[2d\,\,\sin \theta =n\lambda \] waere d = distance between diffracting planes. We can determine the wavelength of these waves,                 \[2\times 4\times {{10}^{-10}}\,\sin \,{{30}^{o}}=\lambda \]                 \[8\times {{10}^{-10}}\times \frac{1}{2}=\lambda \]                 \[4\times {{10}^{-10}}=\lambda \]                 \[\lambda =4\overset{\text{o}}{\mathop{\text{A}}}\,\]


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