In the Davisson-Germer experiment,an electron beam with a wavelength of $1.5 \ \mathring{A}$ is incident normally on a crystal with an atomic spacing of $3 \ \mathring{A}$. At what angle (in degrees) will the first maximum be formed?

Using the Heisenberg uncertainty principle,arrange the following particles in the order of increasing lowest energy possible.
$(I)$ An electron in $H_{2}$ molecule
$(II)$ $A$ hydrogen atom in a $H_{2}$ molecule
$(III)$ $A$ proton in the carbon nucleus
$(IV)$ $A$ $H_{2}$ molecule within a nanotube

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

In the Davisson-Germer experiment,an electron beam of energy $75 \ eV$ falls normally on the surface of a crystal. If the maximum intensity is obtained at an angle of $45^o$ to the direction of the incident beam,then the inter-atomic distance in the lattice plane of the crystal will be .............. $\mathring{A}$

State Heisenberg's uncertainty principle.

In the Davisson and Germer experiment,the velocity of electrons emitted from the electron gun can be increased by