J & K CET Engineering J and K - CET Engineering Solved Paper-2010

  • question_answer
    The mobility of free electrons (charge = e, mass = -m and relaxation time = \[\tau \].) in a metal is proportional to

    A)  \[\frac{e}{m}\tau \]

    B)  \[\frac{m}{e}\tau \]

    C)  \[\frac{e}{m\tau }\]

    D)  \[\frac{m}{e\tau }\]

    Correct Answer: A

    Solution :

    Drift velocity per unit electric field is called mobility of electron, ie,  \[\mu =\frac{{{v}_{d}}}{E}=\frac{E}{\rho neE}\] Now,         \[\rho =\frac{m}{n{{e}^{2}}\tau }\] \[\therefore \] s\[\mu =\frac{n{{e}^{2}}\tau }{mne}=\frac{e\tau }{m}\]


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