7.Photoelectric effect is the emission of photoelectrons from the surface of a metal when electromagnetic radiation of high enough frequency is irradiated.
Certain observations from the photoelectric effect experiment provide evidence for particulate nature of EM radiation.
A minimum threshold frequency is required for photoelectrons to be emitted
since energy of a photon is given by E = hf where f is the frequency of the photon.
[Unlike wave behaviour where intensity determines the amount of energy supplied]
The photoelectrons that were emitted have range of kinetic energy (KE) up till a maximum. This maximum is independent of the intensity of light.
This is because the intensity of light only affects the rate at which photons arrive but the energy of each photon is unchanged.
[Unlike wave behaviour where the KE is expected to continue to increase when intensity increases.]
b)E= work function + Ke max
where E = hf photon energy, work function is the min energy required to extract the electron from the material, Ke max is the maxumum kinetic energy of the photoelectrons.
c)work function = E - Kemax = 3.06 x 10-19 J
d) 3000m
ii) 3000m . Anywhere along the pulse can be the location of the photon hence it ranges from the front to the back of the pulse, hence 3000m
iii) Use uncertainty principle:
uncertainty is p = h/4pi (uncertainty in x) =1.8 x 10-38 Ns
e) Draw the diagram from text showing how the wave function appears after passing through the potential barrier.
[1] A potential barrier is a region containing a field of force that opposes the passage of an incident particle.
[1] If energy E of particle is lower than the barrier energy (height) U, as shown in diagram, the particulate nature does not allow the particle to penetrate through the barrier.
[1] When a particle encounters the barrier, the wave function ψ associated with the wave nature of the particle decreases exponentially with barrier width, as shown in diagram. If this ψ is non-zero beyond the barrier, there is a non-zero probability (α |ψ|2) of finding the particle beyond the barrier. This means that it has tunneled through.
