If the radius of the first Bohr orbit is $r$, then the radius of the second Bohr orbit will be

If the force between the electron in the first Bohr orbit and the nucleus (proton) in a hydrogen atom is $F$,then the force between them when the electron is in the second orbit is

Speed of electron in its $1^{st}$ Bohr's orbit is given by $2.18 \times 10^6 \ m/s$. If the time period of electron in $n^{th}$ orbit is measured as $4.10 \ fs$,the value of $n$ is

Radiation coming from the transition $n = 2$ to $n = 1$ of hydrogen atoms falls on $He^+$ ions in $n = 1$ and $n = 2$ states. The possible transition of helium ions as they absorb energy from the radiation is:

The orbital acceleration of an electron is .........

The ratio of the kinetic energy to the total energy of an electron in a Bohr orbit is