BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    If a conducting rod of length \[4l\] is rotated about at point O in a uniform magnetic field B directed into the paper and \[DE=\text{ I},EA=3I,\]then

    A) \[{{V}_{A}}-{{V}_{E}}=\frac{9}{2}B\omega {{l}^{2}}\]      

    B) \[{{V}_{E}}-{{V}_{A}}=\frac{9}{2}B\omega {{l}^{2}}\]

    C) \[{{V}_{D}}-{{V}_{E}}=\frac{B\omega {{l}^{2}}}{2}\]        

    D) \[{{V}_{A}}-{{V}_{E}}=4B\omega {{l}^{2}}\]

    Correct Answer: D

    Solution :

    Since, \[{{v}_{E}}-{{v}_{D}}=\frac{\Beta \omega l}{2}\times l\] \[{{v}_{E}}-{{v}_{D}}=\frac{B\omega {{l}^{2}}}{2}\]                                           ? (i) \[{{v}_{E}}-{{v}_{A}}=\frac{B\omega 3l}{2}\times 3l=\frac{9B\omega {{l}^{2}}}{2}\]          ? (ii) Subtracting Eq.(i) from Eq. (ii), we get. \[{{v}_{A}}-{{v}_{E}}=4B\omega {{l}^{2}}\] \[\Rightarrow \]\[{{v}_{A}}>{{v}_{E}}\]


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