VIT Engineering VIT Engineering Solved Paper-2015

  • question_answer
    If a line segment OP makes angles of \[\frac{\pi }{4}\] and with X-axis and Y-axis, respectively. Then the direction cosines are

    A) \[\frac{1}{\sqrt{2}},\frac{\sqrt{3}}{2},\frac{1}{\sqrt{2}}\]              

    B) \[\frac{1}{\sqrt{2}},\frac{1}{2},\frac{1}{\sqrt{2}}\]

    C) \[1,\sqrt{3},1\]                 

    D) \[1,\frac{1}{\sqrt{3}},1\]

    Correct Answer: B

    Solution :

    Let \[_{\text{5}}{{\text{Y}}^{\text{10}}}{{\text{=}}_{\text{5}}}{{\text{B}}^{\text{10}}}\],\[{{E}_{n}}=-\frac{13.6}{{{n}^{2}}}eV\] and \[\Rightarrow \] be the angles made by the line segment OP with X-axis,   Y-axis  and Z-axis, respectively. Given          \[34=-\frac{13.6}{{{n}^{2}}}\] \[\Rightarrow \]        \[{{n}^{2}}=4\] \[\Rightarrow \]         \[L=\frac{nh}{2\pi }=\frac{2h}{2\pi }=\frac{h}{\pi }\] \[\because \]           \[\lambda =\frac{h}{p}\] \[\therefore \]           \[\lambda \alpha \frac{1}{p}\] \[\Rightarrow \]            \[\frac{\Delta p}{p}=-\frac{\Delta \lambda }{\lambda }\] \[\therefore \]            \[\left| \frac{\Delta p}{p} \right|=\left| \frac{\Delta \lambda }{\lambda } \right|\] \[\Rightarrow \]             \[\frac{p'}{p}=\frac{0.20}{100}=\frac{1}{500}\] \[\Rightarrow \]                 \[{{E}_{0}}.\] Hence, direction cosines are \[{{E}_{0}}.\]i.e.  \[\Delta {{I}_{C}}=1mA={{10}^{-3}}A\]


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