If the energies of two photons are in the ratio of $3:2$,their wavelengths will be in the ratio of

The wavelength range of the visible spectrum extends from violet $(400 \, nm)$ to red $(750 \, nm).$ Express these wavelengths in frequencies $(Hz).$ $(1 \, nm = 10^{-9} \, m)$

The wavelength (in $\mathring{A}$) of a photon having energy $3 \ eV$ is approximately.
$1 \ eV = 1.6 \times 10^{-12} \ erg$
$h = 6.626 \times 10^{-27} \ erg \ s$
$c = 3 \times 10^{10} \ cm/s$

The wavelength of a spectral line of caesium is $460 \ nm$. What is the frequency of the spectral line?

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 frequency in $Hz$ of orange colour light having wavelength $600 \ nm$. $[c = 3 \times 10^8 \ ms^{-1}]$