NEET AIPMT SOLVED PAPER SCREENING 2009

  • question_answer
    If\[\text{m}{{\text{s}}^{-1}}\] is the force acting on a particle having position vector \[\text{m}{{\text{s}}^{-1}}\] and \[\text{mm}{{\text{s}}^{-1}}\] be the torque of this force about the origin, then

    A) \[3.2\pi \mu V\]and\[4.8\pi \mu V\]      

    B) \[0.8\pi \mu V\]and\[1.6\pi \mu V\]      

    C) \[{{M}^{a}}{{L}^{b}}{{T}^{c}},\]and\[a=1,b=-1,c=-2\]      

    D) \[a=1,b=0,c=-1\]and\[a=1,b=1,c=-2\]

    Correct Answer: C

    Solution :

    Key Idea Torque is an axial vector ie, its direction is always perpendicular to the plane containing vectors \[{{\,}_{Z+}}_{1}^{A}Y\xrightarrow[{}]{{}}\,_{Z-1}^{A-4}\beta +\alpha _{2}^{4}\]and \[_{Z+1}^{A-4}\beta \xrightarrow[{}]{{}}\,_{Z-1}^{A-4}\beta +\gamma _{0}^{0}\] \[{{V}_{A}}=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{\sigma 4\pi {{a}^{2}}}{a}-\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{\sigma 4\pi {{b}^{2}}}{b}\] Torque is perpendicular to both \[+\frac{1}{4\pi {{\varepsilon }_{0}}},\frac{\sigma 4\pi {{c}^{2}}}{c}\]and \[=\frac{\sigma }{{{\varepsilon }_{0}}}(a-b+c)=\frac{\sigma }{{{\varepsilon }_{0}}}(2a)\] \[(\because c=a+b)\]\[{{V}_{B}}=\frac{1}{4\pi {{\varepsilon }_{0}}}-\frac{4\pi {{a}^{2}}}{a}-\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{\sigma 4\pi {{b}^{2}}}{b}\] \[+\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{\sigma 4\pi {{c}^{2}}}{c}\]


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