JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Self Evaluation Test - Dual Nature of Radiation and Matter

  • question_answer
    A particle A of mass m and initial velocity v m collides with a particle B of mass \[\frac{m}{2}\] which is at rest. The collision is head on, and elastic. The ratio of the de-Broglie wavelengths \[{{\lambda }_{A}}\] to \[{{\lambda }_{B}}\] after the collision is        

    A) \[\frac{2}{3}\]

    B) \[\frac{1}{2}\]

    C) \[\frac{1}{3}\]

    D) \[2\]

    Correct Answer: D

    Solution :

    [d] From question, \[{{m}_{A}}=M;m=\frac{m}{2}\] \[{{u}_{A}}=V\text{       }{{u}_{B}}=0\] Let after collision velocity of \[A={{V}_{1}}\] and velocity of \[B={{V}_{2}}\] Applying law of conservation of momentum, \[mu=m{{v}_{1}}+\left( \frac{m}{2} \right){{v}_{2}}\text{ or, 2}\mu \text{=2}{{v}_{1}}\text{ +}{{\text{v}}_{2}}\]            ?.(i) By law of collision \[e=\frac{{{v}_{2}}-{{v}_{1}}}{u-1}\text{ or }u={{v}_{2}}-{{v}_{1}}\]                              ?(ii)                         \[\left[ \because \text{collision is elastic, }e=1 \right]\] using eqns (i) and (11) \[{{v}_{1}}=\frac{1}{3}\mu \text{ and }{{v}_{2}}=\frac{4}{3}u\] De-Broglie wavelength \[\lambda =\frac{h}{p}\] \[\therefore \frac{{{\lambda }_{A}}}{{{\lambda }_{B}}}=\frac{{{P}_{B}}}{{{P}_{A}}}=\frac{\frac{m}{2}\times \frac{4}{3}u}{m\times \frac{1}{3}}=2\]


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