Quantum Phenomena Flashcards
(33 cards)
Are EM waves transverse or longitudinal
Transverse
What phenomenon can be used to show that light can behave as a particle
The photoelectric effect
Describe the photoelectric effect
When light above a frequency is shone on a metal, electrons are released- these electrons are called photoelectrons
What is the threshold frequency
The minimum frequency of required for an electron to be emitted
What is the equation used to determine the energy of a photon
E = HF = HC/lamda
Why does a photon need to have a minimum frequency in order to liberate an electron
The energy of the photon is determined by its frequency, the photons energy must be greater than the work function in order for the bonds to be broken and an electron to be emitted
If a photon has a frequency higher than the threshold frequency, what would occur
The electron would be liberated then the remaining energy would be kinetic energy for the electron
Why cant the threshold frequency be explained by the wave theory
It suggests that any frequency of light should be able to cause photoelectric emission as the energy absorbed be each electron will gradually increase
What theory does explain the photoelectric effect
The photon model
Name one property of the photon model
EM waves travel in discrete packets called photons which have an energy which is directly proportional to frequency
Name another
Each electron can absorb a single photon therefore a photoelectron is only emitted if the frequency is above the threshold frequency
What is the definition of work function
The minimum energy required for electrons to be emitted from the surface of a metal
What is the definition of stopping potential
The potential difference you would need to apply across the metal to stop the photoelectrons with the maximum kinetic energy
What does measuring the stopping potential allow you to find
The maximum kinetic energy released
What do electrons in atoms exist in
Discrete energy levels
How do electrons gain energy
Collisions with free electrons
What’s it called when electrons move up energy levels
Excitation
When they gain enough energy to be removed from the atom, what’s it called
Ionisation
How can ionisation occur
When the energy of the free electron is greater than the ionisation energy
What’s will happen when an electron becomes excited
It will quickly return to its original energy level and therefore release the energy t gained in the form of a photon
What’s a practical use of excitation
Fluorescent tube in order to produce light
What are fluorescent tubes fulled with
Mercury vapour
What happens when a voltage is produced
It accelerates free electrons through the tube which collide with the mercury atoms causing them to become ionised
What’s happened after they’re ionised
More free electrons are released which collide with mercury atoms, causing them to become ionised. When they de-excite they release photons, most are within UV range
