JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Critical Thinking

  • question_answer
    An elementary particle of mass \[m\] and charge \[+e\] is projected with velocity \[v\] at a much more massive particle of charge \[Ze,\] where \[Z>0.\]What is the closest possible approach of the incident particle                     [Orissa JEE 2002]

    A)            \[\frac{Z{{e}^{2}}}{2\pi {{\varepsilon }_{0}}m{{v}^{2}}}\]

    B)                                      \[\frac{Ze}{4\pi {{\varepsilon }_{0}}m{{v}^{2}}}\]

    C)            \[\frac{Z{{e}^{2}}}{8\pi {{\varepsilon }_{0}}m{{v}^{2}}}\]   

    D)            \[\frac{Ze}{8\pi {{\varepsilon }_{0}}m{{v}^{2}}}\]

    Correct Answer: A

    Solution :

               Suppose distance of closest approach is r, and according to energy conservation applied for elementary charge. Energy at the time of projection = Energy at the distance of closest approach Þ \[\frac{1}{2}m{{v}^{2}}=\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{(Ze).e}{r}\Rightarrow r=\frac{Z{{e}^{2}}}{2\pi {{\varepsilon }_{0}}m{{v}^{2}}}\]


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