JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Critical Thinking

  • question_answer
    A particle of mass M at rest decays into two particles of masses m1 and m2, having non-zero velocities. The ratio of the de-Broglie wavelengths of the particles, \[{{\lambda }_{1}}/{{\lambda }_{2}}\]is [IIT-JEE 1999; KCET 2003]

    A)            \[{{m}_{1}}/{{m}_{2}}\]   

    B)            \[{{m}_{2}}/{{m}_{1}}\]

    C)                    1.0                                    

    D)                    \[\sqrt{{{m}_{2}}}/\sqrt{{{m}_{1}}}\]

    Correct Answer: C

    Solution :

                       By law of conservation of momentum                    \[0={{m}_{1}}\overrightarrow{{{v}_{1}}}+{{m}_{2}}\overrightarrow{{{v}_{2}}}\Rightarrow {{m}_{1}}\overrightarrow{{{v}_{1}}}=-{{m}_{2}}\overrightarrow{{{v}_{2}}}\]                    ? ve sign indicates that both he particles are moving in opposite direction. Now de-Broglie wavelengths                    \[{{\lambda }_{1}}=\frac{h}{{{m}_{1}}{{v}_{1}}}\] and \[{{\lambda }_{2}}=\frac{h}{{{m}_{2}}{{v}_{2}}}\]; \[\therefore \ \frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{{{m}_{2}}{{v}_{2}}}{{{m}_{1}}{{v}_{1}}}=1\]


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