JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Electric Field and Potential

  • question_answer
    An electron moving with the speed \[5\times {{10}^{6}}\] per sec is shooted parallel to the electric field of intensity \[1\times {{10}^{3}}N/C\]. Field is responsible for the retardation of motion of electron. Now evaluate the distance travelled by the electron before coming to rest for an instant (mass of \[e=9\times {{10}^{-31}}Kg.\] charge \[=1.6\times {{10}^{-19}}C)\]                               [MP PMT 2003]

    A)            7 m                                           

    B)            0.7 mm

    C)            7 cm

    D)            0.7 cm

    Correct Answer: C

    Solution :

                                 Electric force \[qE=ma\]Þ \[a=\frac{QE}{m}\] \[\therefore \,a=\frac{1.6\times {{10}^{-19}}\times 1\times {{10}^{3}}}{9\times {{10}^{-31}}}=\frac{1.6}{9}\times {{10}^{15}}\] \[u=5\times {{10}^{6}}\] and \[v=0\] \ From \[{{v}^{2}}={{u}^{2}}-2as\] Þ \[s=\frac{{{u}^{2}}}{2a}\] \ Distance \[s=\frac{{{(5\times {{10}^{6}})}^{2}}\times 9}{2\times 1.6\times {{10}^{15}}}\]\[=7\,cm.(\text{approx})\]


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