A sensor is exposed for time $t$ to a lamp of power $P$ placed at a distance $l$. The sensor has a circular opening that is $4d$ in diameter. Assuming all energy of the lamp is given off as light, the number of photons entering the sensor if the wavelength of light is $\lambda $ is $(l >> d)$

A $160 \,W$ light source is radiating light of wavelength $6200 \,\mathring A$ uniformly in all directions. The photon flux at a distance of $1.8 \,m$ is of the order of ………. $m ^{-2} s ^{-1}$ (Planck's constant $\left.=6.63 \times 10^{-34} \,J – s \right)$

Compton effect supports that

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