In a photoelectric effect experiment a light of frequency 1.5 times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be:

When a metal surface is illuminated by light of wavelength $$\lambda$$, the stopping potential is $$8 \mathrm{~V}$$. When the same surface is illuminated by light of wavelength $$3 \lambda$$, stopping potential is $$2 \mathrm{~V}$$. The threshold wavelength for this surface is:

For the photoelectric effect, the maximum kinetic energy $$\left(E_k\right)$$ of the photoelectrons is plotted against the frequency $$(v)$$ of the incident photons as shown in figure. The slope of the graph gives