Quantum theory Flashcards
Wave behaviours of photons:
Refraction
Reflection
Diffraction
Interference
Polarisation
What did Young’s double slit experiment show?
That there was interference of light waves due to constructive and destructive waves.
Sometimes, a peak of one wave will meet a trough of another, resulting in the waves being cancelled out (destructive). Other times, peaks would align with peaks, causing the wave to be further reinforced (constructive).
The bright lights on the wall are from constructive waves and the dark patches between them are from destructive waves.
Why are light waves self-perpetuating?
because an electric field produces a magnetic field and a magnetic field produces an electric field and so on
What is a black body?
An object that absorbs all the incident radiation and then re-emits this usually as a light wave
What is blackbody radiation?
The electromagnetic radiation that is emitted after being heated.
Light comes in:
packets (quanta) according to Planck
Threshold frequency
minimum frequency for electrons to flow from the light that hits a metal
What happens when you increase the intensity of light when below the threshold frequency?
Electrons are not emitted
Frequency increases the energy of photons
Intensity only means more photons are hitting the plate but if these photons dont have enough energy, they wont pass through and emit electrons
What shows that light is a particle?
The photoelectric effect where frequency and intensity are all related to the energy of the photon - proves that light is a discrete packet of energy
What did Rutherford show?
That protons and neutrons are located in the centre of an atom surrounded by electrons that revolve around the nucleus in circular orbits with his gold-foil experiment.
Limitations of Rutherford’s model
No set orbits for electrons
Accelerating charges should emit radiation
Electrons should lose energy and spiral into nucleus according to the model
How did Bohr improve Rutherford’s model?
To resolve the limitation of electrons not spiralling into nucleus, Bohr said that electrons move in specific energy levels based on standing waves. The energy of an electron depends on the size of its orbit
Bohr also stated that radiation is emitted when electron jumps from one energy level to another (electromagnetic radiation)
What is the difference between emission and absorption?
Emission - going down energy levels
Absorption - electron is gaining energy thus moving up an energy level
What is stopping voltage?
Voltage required to stop an electron from being emitted
What is the work function and how do you calculate it?
THe minimum energy required to remove an electron from a solid
W = h*f0 (threshold freq)
