If the momentum of a photon is $p$, then its frequency is

Where $m$ is the rest mass of the photon

Specific heat of water is $4.2 \,J / g ^{\circ} C$. If light of frequency $3 \times 10^9 \,Hz$ is used to heat $400 \,gm$ of water from $20^{\circ} C$ to $40^{\circ} C$, the number of photons needed will be

The value of Planck's constant is

The energy equivalent to $1\,mg$ of matter in $MeV$ is

A source $S_1$ is producing, $10^{15}$ photons per second of wavelength $5000 \;\mathring A.$ Another source $S_2$ is producing $1.02 \times 10^{15}$ photons per second of wavelength $5100\;\mathring A$. Then, $($ power of $S_2)/$  $($ power of $S_1)$ is equal to

The light of two different frequencies whose photons have energies $3.8 \,eV$ and $1.4 \,eV$ respectively, illuminate a metallic surface whose work function is $0.6 \,eV$ successively. The ratio of maximum speeds of emitted electrons for the two frequencies respectivly will be