12th Class Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank MCQs - Dual Nature of Radiation and Matter

  • question_answer
    A proton, a neutron, an electron and an a-particle have same energy. Then, their de-Broglie wavelengths compare as

    A) \[{{\lambda }_{p}}={{\lambda }_{n}}>{{\lambda }_{e}}>{{\lambda }_{a}}\]

    B) \[{{\lambda }_{a}}<{{\lambda }_{p}}={{\lambda }_{n}}>{{\lambda }_{e}}\]

    C) \[{{\lambda }_{e}}<{{\lambda }_{p}}={{\lambda }_{n}}>{{\lambda }_{a}}\]

    D) \[{{\lambda }_{e}}={{\lambda }_{p}}={{\lambda }_{n}}={{\lambda }_{a}}\]

    Correct Answer: B

    Solution :

    Option [b] is correct.
    Explanation: Matter waves (de-Broglie waves) According to de-Broglie, a moving material particle sometimes acts as a wave and sometimes as a particle.
    De- Broglie wavelength: \[{{\lambda }_{d}}=\frac{h}{p}\]
    \[{{\operatorname{E}}_{p}}={{E}_{n}}={{E}_{e}}={{E}_{x}}\]
    \[K.\operatorname{E}.=K=\frac{1}{2}m{{v}^{2}}\]
    \[2K=m{{v}^{2}}\]
    \[2Km={{m}^{2}}{{v}^{2}}\]
    \[2mK={{p}^{2}}\]
    \[\sqrt{2mk=p}\]
    \[\therefore {{\lambda }_{d}}\frac{h}{p}\]
    \[{{\lambda }_{d}}=\frac{h}{\sqrt{2m\operatorname{K}}}\]
    or \[{{\lambda }_{d}}=\frac{h}{\sqrt{2m\operatorname{K}}}\][as h and E(K.E.)is constt.]
    \[\therefore \lambda \propto \frac{1}{\sqrt{m}}\]
    \[{{m}_{a}}>{{m}_{p}}={{m}_{n}}>{{m}_{e}}\]
    \[\therefore {{\lambda }_{a}}<{{\lambda }_{p}}={{\lambda }_{n}}<{{\lambda }_{e}}\]


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