Quantum Physics:
Q. What are photons?
Photons are light particles. They are sometimes referred to
as a quantum of energy of EM radiation.
Q. What is the photoelectric effect?
The photoelectric effect is a phenomenon that occurs when
light of sufficient energy is shone onto a metal surface, causing it to emit
electrons. This effect can cause current to flow. The electrons emitted are
called photoelectrons.
Q. Which features of the photoelectric effect can’t be
explained if light is a wave?
If light were a wave, then the energy possessed by released
electrons would simply increase proportionally with increasing light intensity.
This is not the case. The energy of the released electrons depends on the
frequency of the stimulating light. No electrons are released below a certain frequency:
threshold frequency, no matter how intense the light is.
Q. How does the photon model of light explain the
threshold frequency seen in the photoelectric effect?
Each electron absorbs a single photon. This single photon
must have enough energy to cause an electron to be released; if it doesn’t, the
energy is just re-emitted. The electron can’t build up energy as it could if
light were simply a wave.
Q. What is meant by electron energy levels?
As electrons orbit the nucleus of atoms, they occupy
distinct energy levels. These can be considered analogous to floors on a
building; electrons may occupy a distinct energy level (a floor), but cannot
settle between energy levels (floors).
Q. Why do atoms of different elements have distinct
absorption spectra?
The energy levels, which electrons may occupy, are different
for different elements. Therefore, only distinct energies (and hence
frequencies) of light can be absorbed by each element.
Q. Why do atoms of different elements only emit certain
light frequencies?
When no longer subjected to energy influx, electrons fall
back down to a lower energy level, emitting photons of the same distinct
energies that were originally absorbed. This is useful as it allows us to
identify what elements and with what elemental ratios solar bodies are
comprised, without needing to sample them.
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