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JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Cathode Rays and Positive Rays

  • question_answer
    An electron initially at rest, is accelerated through a potential difference of 200 volt, so that it acquires a velocity \[8.4\times {{10}^{6}}m/s.\] The value of e/m of electron will be                [DPMT 2003]

    A)            \[2.76\times {{10}^{12}}C/kg\]                                        

    B)            \[1.76\times {{10}^{11}}C/kg\]                                        

    C)            \[0.76\times {{10}^{12}}C/kg\]                                        

    D)            None of these

    Correct Answer: B

    Solution :

               \[\frac{1}{2}m{{v}^{2}}=eV\,\,\Rightarrow \,\,\frac{e}{m}=\frac{{{v}^{2}}}{2V}=\frac{{{(8.4\times {{10}^{6}})}^{2}}}{2\times 200}\]\[=1.76\times {{10}^{11}}\,\frac{C}{kg}.\]


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