A photon falls through a height of $1 \,km$ through the earth's gravitational field. To calculate the change in its frequency, take its mass to be $h v / c^{2}$. The fractional change in frequency $v$ is close to
$10^{-20}$
$10^{-17}$
$10^{-13}$
$10^{-10}$
The work function of a substance is $3.0\ \mathrm{eV}$. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately:
The energy equivalent to $1\,mg$ of matter in $MeV$ is
The work function of a metal is