There are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. Can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength.
No, in practice, such stable substances can not be obtained because for the purpose mentioned in the statement these substances will have to supply energy to the photons continuously on their own which is not possible for their stable existence.
Energy conversion in a photoelectric cell takes place from
Photoelectric effect experiments are performed using three different metal plates $\mathrm{p}, \mathrm{q}$ and $\mathrm{r}$ having work functions $\phi_p=2.0 \mathrm{eV}, \phi_q=2.5 \mathrm{eV}$ and $\phi_r=3.0 \mathrm{eV}$, respectively. A light beam containing wavelengths of $550 \mathrm{~nm}, 450 \mathrm{~nm}$ and $350 \mathrm{~nm}$ with equal intensities illuminates each of the plates. The correct I-V graph for the experiment is [Take $h c=1240 \mathrm{eV} \mathrm{nm}$ ]
A $100\,watt$ light source is emitting radiations of wavelength $5000\,\mathop A\limits^o $. The rate of emission of photons is of the order of
A $10\, kW$ transmitter emits radio waves of wavelength $500\, m$. The number of photons emitted per second by the transmitter is of the order of