Monochromatic light of frequency $6.0 \times 10^{14} \text{ Hz}$ is produced by a laser. The power emitted is $2 \times 10^{-3} \text{ W}$. The number of photons emitted,on the average,by the source per second is

Consider two black bodies $A$ and $B$ having equal surface areas. On the surface of $A$, $n$ photons of frequency $f$ are incident perpendicularly in a time $t$. On the surface of $B$, $2n$ photons of frequency $3f$ are incident perpendicularly in a time $4t$. The ratio of average intensity of radiation on surface $A$ to that on surface $B$ is

The frequency of a photon having energy $66 \ eV$ is:

Two sources of light emit with a power of $200 \ W$. The ratio of the number of photons of visible light emitted per second by each source having wavelengths $300 \ nm$ and $500 \ nm$ respectively,will be:

$A$ gamma ray photon creates an electron-positron pair. If the rest mass energy of an electron is $0.5\, MeV$ and the total kinetic energy $(K.E.)$ of the electron-positron pair is $0.78\, MeV$,then the energy of the gamma ray photon must be.......$MeV$.

What is called as the quantum of energy? What is its energy?