The ratio of the energy of a photon with wavelength $3000 \ \mathring{A}$ to that of a photon with wavelength $6000 \ \mathring{A}$ is:

Which of the following series of emission spectral lines for hydrogen is observed in the visible region?

The energy of one mole of photons of radiation whose frequency is $5 \times 10^{10} \, s^{-1}$ is .......... $J$.

The number of the following statements which is/are incorrect is:
$A$. Line emission spectra are used to study the electronic structure.
$B$. The emission spectra of atoms in the gas phase show a continuous spread of wavelength from red to violet.
$C$. An absorption spectrum is like the photographic negative of an emission spectrum.
$D$. The element helium was discovered in the sun by spectroscopic method.

Calculate the wavelength of yellow light having a frequency of $5.09 \times 10^{14} \ Hz$.

Nitrogen laser produces a radiation at a wavelength of $337.1 \ nm$. If the number of photons emitted is $5.6 \times 10^{24}$,calculate the power of this laser.