Quantum Physics Flashcards
What is the Photoelectric Effect?
The photoelectric effect is the emission of photoelectrons from a metal surface when electromagnetic radiation of a sufficiently high frequency is incident on it.
What does the work function of a metal mean?
The work function of a metal is the minimum amount of energy that will remove an electron from the surface of the metal.
What does threshold frequency mean?
The threshold frequency is the minimum frequency of an incident photon that will remove an electron from the surface of the metal.
What does the stopping potential suggest?
The stopping potential is the minimum potential difference between the metal and collector that will prevent an ejected photoelectron from reaching the collector.
How does the existence of line spectra provide convincing evidence for the existence of discrete electron energy levels in isolated atoms?
As each line of the line spectrum corresponds to a single wavelength, and hence a single frequency, of light, this implies that the energies of the photons emitted are discrete. This is only possible if the energy levels of electrons within the atom are discrete as well.
Define energy level in an atom.
An energy level is the quantized energy corresponding to an allowed state (or orbital) of the electron within the atom.
What is the range of wavelength of X-rays?
0.001nm to 10nm
What is the Heisenberg Uncertainty Principle?
The Heisenberg Uncertainty Principle states that it is impossible to measure the exact position and momentum at the same (i.e. cannot both be zero).
What is meant by a photon?
A photon is a small discrete quantum of electromagnetic energy where the energy of a single photon is directly proportional to its frequency. E=hf
With reference to the photoelectric effect, explain why the existence of a threshold frequency provides evidence for the particulate nature of electromagnetic radiation.
The photoelectric effect is only observed when the frequency of the electromagnetic radiation incident in a particular metal is at least a minimum frequency. It does not depend on the intensity of the radiation. This is the threshold frequency and each metal has its own threshold frequency. This can only be explained if electromagnetic radiation is made up of discrete quanta of energy known as photons. The energy of each photon is hf, where h is the Planck constant and f is the frequency of the radiation. An electron in the metal requires a minimum energy to leave the surface of the metal in the photoelectric effect. This minimum energy is the work function of the metal. The electron absorbs energy only from one photon in the particulate theory. Hence for photo emission to occur, the energy of each photon hf >= ø. The minimum frequency f = ø/h is the threshold frequency.
