NEET Sample Paper NEET Sample Test Paper-7

  • question_answer
    Three points charges \[q-2q\] and \[-2q\] are placed at the verticles of an equilateral traingle of side a. The work done by some external forces to slowly increase their separation to 2a will be:

    A)  \[\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{2{{q}^{2}}}{a}\]                

    B)  \[\frac{{{q}^{2}}}{4\pi {{\varepsilon }_{0}}a}\]

    C)  \[\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{3{{q}^{2}}}{3R}\]                   

    D)  zero

    Correct Answer: D

    Solution :

    As potential energy of the system initially and finally are given by \[{{U}_{i}}=\frac{(q)(-2q)+(q)(-2q)+(-2q)(-2q)}{4\pi {{\varepsilon }_{0}}a}=0\] and \[{{U}_{f}}=\frac{(q)(-2q)+(q)(-2q)+(-2q)(-2q)}{4\pi {{\varepsilon }_{0}}(2q)}=0\]As,    \[\Delta U=0\] \[{{w}_{ext}}=0\]


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