Monochromatic light of frequency $6 \times 10^{14} \mathrm{~Hz}$ is produced by a laser. The power emitted is $2 \times 10^{-3} \mathrm{~W}$. How many photons per second on an average, are emitted by the source?

(Given $\mathrm{h}=6.63 \times 10^{-34} \mathrm{Js}$ )

Both the nucleus and the atom of some element are in their respective first excited states. They get de-excited by emitting photons of wavelengths $\lambda _N,\,\lambda _A$  respectively. The ratio $\frac{{{\lambda _N}}}{{{\lambda _A}}}$  is closest to

A point source is emitting sound waves of intensity $16 \times 10^{-8} \mathrm{Wm}^{-2}$ at the origin. The difference in intensity (magnitude only) at two points located at a distances of $2 \mathrm{~m}$ and $4 \mathrm{~m}$ from the origin respectively will be______ $\times 10^{-8} \mathrm{Wm}^{-2}$

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

Assertion : The energy $(E)$ and momentum $(p)$ of a photon are related by $p = E/c$.
Reason : The photon behaves like a particle.