JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves JEE PYQ-Photo Electric Effect X-rays

  • question_answer
    Two electrons are moving with non-relativistic speeds perpendicular to each other. If corresponding de Broglie wavelengths  are \[{{\lambda }_{1}}\] and \[{{\lambda }_{2}}\], their de Broglie wavelength in the frame of reference attached to their centre of mass is:                          [JEE Online 15-04-2018]

    A) \[{{\lambda }_{CM}}={{\lambda }_{1}}={{\lambda }_{2}}\]

    B) \[\frac{1}{{{\lambda }_{CM}}}=\frac{1}{{{\lambda }_{1}}}+\frac{1}{{{\lambda }_{2}}}\]

    C) \[{{\lambda }_{CM}}=\frac{2{{\lambda }_{1}}{{\lambda }_{2}}}{\sqrt{{{\lambda }_{1}}^{2}+{{\lambda }_{2}}^{2}}}\]

    D) \[{{\lambda }_{CM}}=\left( \frac{{{\lambda }_{1}}+{{\lambda }_{2}}}{2} \right)\]

    Correct Answer: B

    Solution :

    [b] Since
    \[\lambda =\frac{h}{mv}\]
    \[v=\frac{h}{m\lambda }\]
    Let \[{{v}_{1}}\] and \[{{v}_{2}}\] are the speeds of electrons
    \[{{v}_{cm}}=\frac{{{v}_{1}}+{{v}_{2}}}{2}\]
    \[\frac{h}{2m{{\lambda }_{cm}}}=\frac{1}{2}(\frac{h}{m{{\lambda }_{l}}}+\frac{h}{m{{\lambda }_{2}}})\]
    \[\frac{1}{{{\lambda }_{cm}}}=\frac{1}{{{\lambda }_{1}}}+\frac{1}{{{\lambda }_{2}}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner