Question: Q. 2. Write briefly the underlying principle used in Davisson-Germer experiment to verify wave nature of electrons experimentally. What is the de-Broglie wavelength of an electron with kinetic energy (K.E.) $120 \mathrm{eV}$ ?
U] [OD South 2016]
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Solution:
Ans. Diffraction effects are observed for beams of electrons scattered by the crystals.
$$ \begin{aligned} & \lambda=\frac{1.227 \mathrm{~nm}}{\sqrt{\mathrm{V}}} \ & \lambda=\frac{1.227 \mathrm{~nm}}{\sqrt{120}} \ & \lambda=0.112 \mathrm{~nm} \end{aligned} $$
Alternatively,
$$ \begin{aligned} & \lambda=\frac{h}{\sqrt{2 m e V}} \ & \lambda=\frac{6.63 \times 10^{-34}}{\sqrt{2 \times 9.1 \times 10^{-31} \times 1.6 \times 10^{-19} \times 120}} \ & \lambda=0.112 \mathrm{~nm} \end{aligned} $$
