List of top Atomic and Molecular Physics Questions on atom structure models asked in GATE PH

The mean distance between the two atoms of an HD molecule is \( r \), where H and D denote hydrogen and deuterium, respectively. The mass of the hydrogen atom is \( m_H \). The energy difference between the two lowest lying rotational states of HD in multiples of \(\frac{h^2}{m_H r^2}\) is:

Crystal structures of two metals A and B are two-dimensional square lattices with same lattice constant a. Electrons in metals behave as free electrons. The Fermi surfaces corresponding to A and B are shown by solid circles in figures.

The electron concentrations in A and B are \( n_A \) and \( n_B \), respectively. The value of \((n_B / n_A)\) is: