If $h$ is Planck's constant in $SI$ system,the momentum of a photon of wavelength $0.01 \, \mathring{A}$ is:

What is a photon?

$A$ parallel beam of light of wavelength $900 \, nm$ and intensity $100 \, W/m^2$ is incident on a surface perpendicular to the beam. The number of photons crossing $1 \, cm^2$ area perpendicular to the beam in one second is:

If the energy of a photon with wavelength $6000 \ \mathring{A}$ is $3.32 \times 10^{-19} \ J$, then the energy of a photon with wavelength $4000 \ \mathring{A}$ is ............. $eV$.

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

Positron is the antiparticle of