The minimum intensity of light to be detected by human eye is ${10^{ - 10}}W/{m^2}$. The number of photons of wavelength $5.6 \times {10^{ - 7}}m$ entering the eye, with pupil area ${10^{ - 6}}{m^2}$, per second for vision will be nearly

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

If $5\%$ of the energy supplied to a bulb is irradiated as visible light, how many quanta are emitted per sec by a $100$ $watt$ lamp ? Assume wavelength of visible light as $5.6\times10^{-5}\, cm$.

The threshold wavelength for photoelectric emission from a material is $5500\,\mathring A$. Photoelectrons will be emitted, when this material is illuminated with monochromatic radiation from a

$A.$ $75\,W$ infra-red lamp

$B.$ $10\,W$ infra-red lamp

$C.$ $75\,W$ ultra-violet lamp

$D.$ $10\,W$ ultra-violet lamp

Choose the correct answer from the options given below :

In a photoemissive cell with executing wavelength $\lambda $, the fastest electron has speed $v.$ If the exciting wavelength is changed to $\frac{{3\lambda }}{4}$, the speed of the fastest emitted electron will be

A photon, an electron and a uranium nucleus all have the same wavelength. The one with the most energy