Q.

The de-Broglie wavelength of an electron is the same as that of a photon. If velocity of electron is 25 % of the velocity of light, then the ratio of K.E. of electron and K.E. of photon will be             [2024]

1 1/1  
2 1/8  
3 8/1  
4 1/4  

Ans.

(2)           

              For photon, Ep=hcλpλp=hcEp

                For electron, λe=hmeve=hve2Ke

                Given ve=0.25c

                           λe=h×0.25c2Ke=hc8Ke

                 Also hcEp=hc8KeKeEp=18