JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Self Evaluation Test - Electric Chages and Fields

  • question_answer
    Three charges \[{{q}_{1}},\text{ }+{{q}_{2}}\] and \[{{q}_{3}}\]are place as shown in the figure. The x-component of the force on\[-{{q}_{1}}\]is proportional to

    A) \[\frac{{{q}_{2}}}{{{b}^{2}}}-\frac{{{q}_{3}}}{{{a}^{2}}}\cos \theta \]

    B) \[\frac{{{q}_{2}}}{{{b}^{2}}}+\frac{{{q}_{3}}}{{{a}^{2}}}\sin \theta \]

    C)  \[\frac{{{q}_{2}}}{{{b}^{2}}}+\frac{{{q}_{3}}}{{{a}^{2}}}\cos \theta \]

    D) \[\frac{{{q}_{2}}}{{{b}^{2}}}-\frac{{{q}_{3}}}{{{a}^{2}}}\sin \theta \]  

    Correct Answer: B

    Solution :

    [b] Force on charge \[{{q}_{1}}\], due to \[{{q}_{2}}\] is \[{{F}_{12}}=k\frac{{{q}_{1}}{{q}_{2}}}{{{b}^{2}}}\] Force on charge \[{{q}_{1}}\]due to \[{{q}_{3}}\] is \[{{F}_{13}}=k\frac{{{q}_{1}}{{q}_{3}}}{{{a}^{2}}}\] The X- component of the Force \[\left( {{F}_{x}} \right)\] on \[{{q}_{1}}\]is \[{{F}_{12}}+{{F}_{13}}\sin \theta \] \[\therefore \,\,\,\,\,{{F}_{x}}=k\frac{{{q}_{1}}{{q}_{2}}}{{{b}^{2}}}+k\frac{{{q}_{1}}{{q}_{2}}}{{{a}^{2}}}\sin \theta \] \[\therefore {{F}_{x}}\propto \frac{{{q}_{2}}}{{{b}^{2}}}+\frac{{{q}_{3}}}{{{a}^{2}}}\sin \theta \]


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