In hydrogen atoms, the radius of the smallest orbit of the electron is $a_0$. The radius of the third orbit is:

In the Bohr model of a hydrogen atom,the centripetal force is furnished by the Coulomb attraction between the proton and the electron. If ${a_0}$ is the radius of the ground state orbit,$m$ is the mass,$e$ is the charge on the electron,and ${\varepsilon _0}$ is the vacuum permittivity,the speed of the electron is:

What is ground state?

Explain Bohr's atomic model.

Using Bohr's atomic model,derive an equation for the radius of the $n^{th}$ orbit of an electron.

In a hydrogen atom, the electron makes $6.6 \times 10^{15}$ revolutions per second around the nucleus in an orbit of radius $0.5 \times 10^{-10} \, m$. This is equivalent to a current of nearly: