$A$ parallel beam of electrons travelling in $x-$ direction falls on a slit of width $d$. If after passing the slit,an electron acquires momentum $P_y$ in the $y-$ direction,then for a majority of electrons passing through the slit ($h$ is Planck's constant):

The wave nature of electrons suggests that they will produce diffraction effects. Davisson and Germer experimentally proved this by diffracting electrons from a crystal. The law of diffraction from a crystal is obtained from the constructive interference of electron waves reflected from the planes of atoms in the crystal. When electrons are incident on the crystal plane at an angle $i$ with the normal to the plane,and the distance between the planes is $d$,which of the following equations can be used to calculate the de Broglie wavelength of the electrons if a sharp diffraction peak is obtained?

Which of the following statements is incorrect regarding the Davisson-Germer experiment?

$A$ sodium atom is in one of the states labeled 'Lowest excited levels'. It remains in that state for an average time of $10^{-8} \, s$,before it makes a transition back to a ground state. What is the uncertainty in energy of that excited state?

Explain Heisenberg's uncertainty principle.

In the Davisson-Germer experiment,the nickel crystal acts as a .........