Achieve an A* in your A Level Physics exams with our expertly written notes on 'Quantum Phenomena'. Created by a student who scored an A*, these notes are clear and easy to understand. Explore the fascinating world of quantum physics, covering topics such as the photoelectric effect, energy levels,...
Ionisation & Excitation
Electron volt def.?
- the kinetic energy of an electron after it has been accelerated through a potential difference
of 1 volt
Ionisation def.?
- when electron are given sufficient energy, they leave their atom completely (producing an
ion - hence ionisation)
Excitation def.?
- when electrons are given sufficient energy to move up 1 or more energy levels (but stay
inside their atom)
Diagram of a fluorescent tube?
Which component of the fluorescent tube is where visible light is coming from?
- phosphor coating
(not the cathode ← that’s where we have the electrons that we shine light onto)
- the photons emitted from the mercury atoms are part of the UV spectrum (they have high
energy)
→ the electrons in the powder absorb the photons
→ this changed the frequency if the photons
→ the powder then emits photons in the visible spectrum as the electrons in the powder
de-excite
Ground state definition?
- the lowest energy level available for electrons to occupy
If an electron de-excites from n = 3, what is the max. no. of photons that could be emitted?
-2
, How do excited electrons emit photons?
- they de-excite
- this emits a photon of energy equal to the energy difference between the 2 levels
For a photon to excite an electron, the photon must have an exact amount of energy.
Why?
- energy is needed for an electron to move to a higher energy level
- this excitation requires an exact amount of energy:
→ the photon’s energy must be equal to the difference between the energy levels it
transitions between
→ then, in a one to one interaction, all of the photon’s energy will be absorbed
When electrons are de-excited, why do the emitted photons have discrete
frequencies?
- protons are emitted when an electron falls from one FIXED energy level to another FIXED
energy level
- the photon is given a specific amount of energy
- this energy the photon has is directly proportional to frequency as E = hf → emitted
photons therefore have discrete frequencies
Why are the frequencies of these transitions form the equation: f1 = f2 + f3 (f1 being
the highest f)?
- a = f1, b = f3, c = f2
→ the released energy of A has to be the sum of the released energies from B and C,
therefore → hf1 = hf2 + hf3 → cancel h: f1 = f2 + f3
What does it mean that an electron is at an energy level of 0 eV?
- the atom has been ionised
- enough energy has been transferred to the electron, so that it could escape the
electrostatic forces of the atom
- the electron is no longer bounded by the electrostatic force from the nucleus
First excitation energy def.?
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