NEET AIPMT SOLVED PAPER SCREENING 2006

  • question_answer
                    Given:   The mass of electron is \[9.11\times {{10}^{-31}}kg\]                                 Planck constant is \[6.626\,\times {{10}^{-34}}Js,\]                 the uncertainty involved in the measurement of velocity within a distance of 0.1 \[\overset{\text{o}}{\mathop{\text{A}}}\,\] is :

    A)                 \[5.79\times {{10}^{6}}m{{s}^{-1}}\]

    B)                 \[5.79\times 10\,m{{s}^{-1}}\]

    C)                         \[5.79\times {{10}^{8}}\,m{{s}^{-1}}\]

    D)                 \[579\,\times {{10}^{5}}\,m{{s}^{-1}}\]

    Correct Answer: A

    Solution :

                    By Heisenberg's uncertainty principle                 \[\Delta p\times \Delta x\ge \frac{h}{4\pi }\]                 or            \[\Delta v\times \Delta x\ge \frac{h}{4\pi m}\]                 \[\Delta p\to \,\]uncertainty in momentum                 \[\Delta x\to \,\]uncertainty in position                 \[\Delta v\to \,\]uncertainty in velocity                 \[m\to \,\]mass of particle                 Given that,                 \[\Delta x=0.1\,{\AA}=0.1\times {{10}^{-10}}\,m\]                 \[\Delta x=0.1\,{\AA}=0.1\times {{10}^{-10}}\,m\]                 \[m=9.11\times {{10}^{-31}}\,kg\]                 \[h=Planck\,\text{constant}\,=6.626\times {{10}^{-34}}\,Js\]                 \[\pi =3.14\]                 In uncertain position \[\Delta v\times \Delta x=\frac{h}{4\pi m}\]                 \[\Delta v\times 0.1\times {{10}^{-10}}=\frac{6.626\times {{10}^{-34}}}{4\times 3.14\times 9.11\times {{10}^{-31}}}\]                 \[\Delta v=\frac{6.626\times {{10}^{-34}}}{4\times 3.14\times 9.11\times {{10}^{-31}}\times 0.1\times {{10}^{-10}}}\,m{{s}^{-1}}\]                 \[=5.785\times {{10}^{6}}\,m{{s}^{-1}}\]                 \[=5.79\times {{10}^{6}}\,m{{s}^{-1}}\]


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