A $200\, W$ sodium street lamp emits yellow light of wavelength $0.6\, \mu m$. Assuming it to be $25\%$ efficient in converting electrical energy to light, the number of photon of yellow light it emits per second is
$1.5 \times 10^{20}$
$62 \times 10^{20}$
$3 \times 10^{19}$
$6 \times 10^{18}$
If a photon has velocity $c$ and frequency $\nu$, then which of following represents its wavelength
What is the energy of photon whose wavelength is $6840\,\mathop A\limits^o $ ?......$eV$
The momentum of the photon of wavelength $5000\,\mathring A$ will be
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