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 $.........\times 10^{-17} kg\,m / s$

If the energy of the photon is increased by a factor of $4$, then its momentum

The work function of a metal is

Two metallic plates $A$ and $B$, each of area $5 ×10^{-4}m^2$ are placed parallel to each other at a separation of $1\ cm$. Plate $B$ carries a positive charge of $33.7 \,pc$. $A$ monochromatic beam of light, with photons of energy $5\, eV$ each, starts falling on plate $A$ at $t = 0$, so that $10^{16}$ photons fall on it per square meter per second. Assume that one photoelectron is emitted for every $10^{6}$ incident photons. Also assume that all the emitted photoelectrons are collected by plate $B$ and the work function of plate $A$ remains constant at the value $2\, eV$. Electric field between the plates at the end of $10$ seconds is

A $160 \,W$ infrared source is radiating light of wavelength $50000 \,\mathring A$ uniformly in all directions. The photon flux at a distance of $1.8 \,m$ is the order of ............. $m^{-2} s ^{-1}$

A totally reflecting small plane mirror placed horizontally faces a parallel beam of light as hown in figure. The mass of mirror is $20\, gm$. Assume that there is no absorption in the lens and that $30\%$ of the light emitted by the source goes through the lens. Find the power of the source needed to support the weight of the mirror ............... $MW$ (take $g = 10\, m/s^2$) :-