The existence of a positively charged nucleus was established by:

Circumference of the first orbit of hydrogen atom is given by the formula :

Supposing the energy (in arbitrary units) of the energy levels in the hydrogen atom is given as under:

Energy level	$K$ $(n=1)$	$L$ $(n=2)$	$M$ $(n=3)$	$N$ $(n=4...n=\infty)$
Energy	$-864 \ a.u.$	$-216 \ a.u.$	$-96 \ a.u.$	$0 \ a.u.$

The excitation energy needed to raise the electron from $M$ level to $n = \infty$ would be:

If the speed of an electron in the Bohr's first orbit of a hydrogen atom is $x$,the speed of the electron in the third Bohr's orbit is:

Find the energy of a photon having a wavelength of $6000 \ \mathring{A}$. (Given: $h = 6.62 \times 10^{-27} \ erg \cdot s$)

The wavelength of the first line of the Balmer series in the hydrogen spectrum is ................ $\mathring{A}$.