NEET Questions Solved

NEET - 2016

Electrons of mass m with de-Brogile wavelength λ fall on the target in an X-ray tube. The cut off wavelength λ0 of the emitted X-ray is

(a) λ0=2mcλ2h          (b) λ0=2hmc

(c) λ0=2m2c2λ3h2       (d) λ0=λ

(a) Key idea Cut-off wavelength occurs when incoming electron looses its complete energy in collision. This energy appears in the form of X-rays.

Given, mass of electrons=m

    de-Broglie wavelength=λ

So, kinet energy, of  electron = p22m


Now, maximum energy of photon can be given by

E=hcλ0=h22mλ2λ0=hc×2λ2mh        = 2mcλ2h

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