JEE Main & Advanced JEE Main Paper (Held On 19 May 2012)

  • question_answer
    If the kinetic energy of an electron is increased four times, the wavelength of the de-Broglie wave associated with it would become     JEE Main  Online Paper (Held On 19  May  2012)

    A) one fourth        

    B)                        half

    C)                        four times          

    D)                        two times

    Correct Answer: B

    Solution :

                    de - Broglie wavelength is given by : \[\lambda =\frac{h}{mv}\]                                                           ...(i) \[K.E.=\frac{h}{2}m{{v}^{2}}\] \[{{v}^{2}}=\frac{2KE}{m}\] \[v=\sqrt{\frac{2KE}{m}}\] Substituting this in equation (i) \[\lambda =\frac{h}{m}\sqrt{\frac{m}{2KE}}\] \[\lambda =h\sqrt{\frac{1}{2m(K.E.)}}\]i.e.\[\lambda =\propto \frac{1}{\sqrt{KE}}\] \[\therefore \]when KE become 4 times wavelength become 1/2.


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