The energy of one mole of photons of radiation of frequency $2 \times 10^{12} \ Hz$ in $J \ mol^{-1}$ is $.....$ (Nearest integer) (Given: $h = 6.626 \times 10^{-34} \ Js$,$N_A = 6.022 \times 10^{23} \ mol^{-1}$)

What is the wavelength for a wave having frequency $50 \ Hz$?

$\alpha$-rays have

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

Which of the following statements is correct about the photoelectric effect?
$1$. The number of electrons ejected from a metal surface is inversely proportional to the intensity of light.
$2$. Below the threshold frequency,the photoelectric effect can be observed.
$3$. At a frequency higher than the threshold frequency,the ejected electrons have a certain kinetic energy.
$4$. At a frequency higher than the threshold frequency,the electron is still on the metal surface.

The wavelength of blue light is $480 \ nm$. What is the frequency of this light?