RAJASTHAN PMT Rajasthan - PMT Solved Paper-2010

  • question_answer
    If 10000 V is applied across an X-ray tube, what will be the ratio of de-Broglie wavelength of the incident electrons to the shortest wavelength of X-ray produced? (e/m for electron is \[1.8\,\times {{10}^{11}}Ck{{g}^{-1}}\])

    A)  1                                            

    B)  0.1

    C)  0.2                        

    D)         0.3

    Correct Answer: B

    Solution :

    For the incident electron                 \[\frac{1}{2}m{{v}^{2}}=eV\]or\[{{p}^{2}}=2meV\] \[\therefore \]de-Broglie wavelength\[{{\lambda }_{1}}=\frac{h}{p}=\frac{h}{\sqrt{2meV}}\] Shortest \[X-\]ray wavelength\[{{\lambda }_{2}}=\frac{hc}{eV}\] \[\therefore \]  \[\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{1}{c}\sqrt{\left( \frac{V}{2} \right)\left( \frac{e}{m} \right)}=\frac{\sqrt{\frac{{{10}^{4}}}{2}\times 1.8\times {{10}^{11}}}}{3\times {{10}^{8}}}\]                      \[=0.1\]


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