The radius of the $2^{nd}$ orbit of $Li^{2+}$ is $x$. The expected radius of the $3^{rd}$ orbit of $Be^{3+}$ is:

On the basis of Bohr's model,the radius of $3^{rd}$ orbit is

The ratio of the time period of an electron in the first and third orbit of an $H$-atom would be:

$A$ $150 \ W$ bulb emits light of wavelength $6600 \ \mathring{A}$ and only $8 \%$ of the energy is emitted as light. How many light photons are emitted by the bulb per second?

When electromagnetic radiation of wavelength $310 \ nm$ falls on the surface of a metal having work function $3.55 \ eV$, the velocity of photoelectrons emitted is $x \times 10^5 \ ms^{-1}$. The value of $x$ is (Nearest integer). Given: $m_{e} = 9 \times 10^{-31} \ kg$, $h = 6.63 \times 10^{-34} \ J \cdot s$, $c = 3 \times 10^8 \ m/s$, $1 \ eV = 1.6 \times 10^{-19} \ J$.

If the wavelength of light is $5.89 \times 10^{-5} \ cm$,then the energy of one photon in the given light will be ......