J & K CET Engineering J and K - CET Engineering Solved Paper-2004

  • question_answer
    A particle with rest mass zero is moving with speed c. The de-Broglie wavelength associated with it

    A)  zero          

    B)  infinity

    C)  \[\frac{hv}{c}\]       

    D)  \[\frac{{{m}_{0}}c}{h}\]

    Correct Answer: A

    Solution :

    The de-Broglie wavelength \[(\lambda )\] is given by             \[\lambda =\frac{h}{p}\]            ...(i) where h is Planck's constant, p the momentum. Also,     \[p=mv=\frac{{{m}_{0}}}{\sqrt{1-\frac{{{v}^{2}}}{{{C}^{2}}}}}\] ...(ii) where \[{{m}_{0}}\] is rest mass, v the velocity and c the speed of light. From Eqs. (i) and (ii), we get \[\lambda =\frac{h\sqrt{1-\frac{{{v}^{2}}}{{{c}^{2}}}}}{{{m}_{0}}v}\] Given: \[v=c\] \[\therefore \] \[\lambda =0\]


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