A beam of light of wavelength $400\,nm$ and power $1.55\,mW$ is directed at the cathode of a photoelectric cell. If only $10 \%$ of the incident photons effectively produce photoelectron, then find current due to these electrons $………..\mu A$

[given, $hc =1240\,eV – nm , e =1.6 \times 10^{-{ }^{19}\,C }$ )

The beam of light has three wavelengths $4144 \,\mathring A$, $4972 \;\mathring A$ and $6216\; \mathring A$ with a total intensity of $3.6 \times$ $10^{-5}\,Wm ^2$ equally distributed amongst the three wavelengths. The beam falls normally on the area $1\,cm ^2$ of a clean metallic surface of work function $2.3\,eV$. Assume that there is no loss of light by reflection and that each energetically capable photon ejects one electron. Calculate the number of photoelectrons liberated in $2\,s$.

An important spectral emission line has a wavelength of $21 cm$. The corresponding photon energy is

$(h = 6.62 \times {10^{ – 34}}Js;\;\;c = 3 \times {10^8}m/s)$

A small object at rest, absorbs a light pulse of power $20\,mW$ and duration $300\,ns$. Assuming speed of light as $3 \times 10^8\,m / s$. the momentum of the object becomes equal to $………\times 10^{-17} kg\,m / s$

Rest mass energy of an electron is $0.51\  MeV.$ If this electron is moving with a velocity $0.8\ c$ (where $c$ is velocity of light in vacuum), then kinetic energy of the electron should be. ……….. $MeV$