In an experiment where the type of metal,intensity of light and potential difference across a battery is kept constant at 2V the results show that an increase in wavelength, obviously in turn decreases the frequency, causes the current of the circuit to decrease (eventually to 0A). what would be the direct cause for the current to become zero? i understand that with the increased wavelength there will be less energy supplied to the metal surface causing the emitted electrons to decrease but does this lack of energy cause the current to become zero?
The photoelectric effect is usually explained in the following way: photons come in from some source and knock electrons out of the metal. These electrons then make up a current through the circuit.
When the photons do not have enough energy to knock out an electron, there will be no electrons to go around the circuit. This causes the current to go to zero.
The important part of this experiment should be that there's a relatively sharp cutoff. "Classical" theory would say that the probility of electron ejection is proportional to the energy density, so a high-power long wavelength source would produce the same energy as a low-power, short wavelength source. In fact, photons below a certain energy level cannot eject electrons at all. This was one of the breakthrough experiments which showed that photons, or quantized packets of light energy, exist.