The wavelengths of ${K_\alpha }$ $X-$ rays of two metals $'A'$ and $'B'$ $\frac{4}{{1875R}}$ and $\frac{1}{{675R}}$ respectively, where $'R'$ is Rydberg's constant. The number of elements lying between $'A'$ and $'B'$ according to their atomic numbers is
$3$
$6$
$5$
$4$
What is the atomic number of gold ?
The radius of the smallest electron orbit in hydrogen-like ion is $(0.51/4 \times 10^{-10})$ metre; then it is
If the force between the electron in the first Bohr orbit and the nucleus (proton) in hydrogen atom is $F$, then the force between them when the electron is in the second orbit is
An $X-$ ray tube is operated at $50\, kV$. the minimum wavelength produced is.......$\mathop A\limits^o $
The radius of a nucleus is given by $r_0 A^{1 / 3}$, where $r_0=1.3 \times 10^{-15} \,m$ and $A$ is the mass number of the nucleus. The lead nucleus has $A=206$. The electrostatic force between two protons in this nucleus is approximately ................ $N$