Quantum Physics Flashcards
What is a photon
A packet of discrete energy
Why was the idea of a photon developed
Wave theory could not explain the photoelectric effect
What did Einstein assume that the energy of a photon depend on
Its frequency
E =hf
How did Planck solve the Ultraviolet Catastrophe
Introduced the idea that the energy of vibrating atoms can only be in multiples of a basic amount - a quantum of energy
What is the ultraviolet catastrophe
The incorrect prediction that the intensity of radiation from an object should become infinite at smaller and smaller wavelengths according to wave theory
What do lasar beams consist of
Photons of the same frequency
What is the power of a laser beam
Nhf where N is the number of photons passing a point every second
Photoelectric Effect definition
The emission of electrons from the surface of a metal when it is illuminated by EM radiation above a certain threshold frequency
Observations of the Photoelectric Effect
Emissions of electrons only occur if the frequency of incident EM radiation is above a certain threshold frequency no matter the intensity
Incident EM radiation of frequency above the threshold frequency results in the instantaneous emission of electrons
Increasing the intensity of incident radiation increases the number of electrons emitted per second not the KE as long as above threshold frequency
Photoelectric Effect Explanations
Wave theory suggests that electrons should gain energy from incoming radiation over time - independent of intensity and frequency - thus at any frequency of incident radiation emission of electrons should eventually occur
Observations can be explained by considering light to be composed of photons of a discrete amount of energy - dependent upon frequency of the EM radiation
What is the work function
Minimum amount of energy needed by an electron to escape a metal surface
What does increasing intensity of incident EM radiation do
Increasing intensity of incident EM radiation increases number of photons passing per unit time, increasing the number of photon-electron interactions per unit time, increasing the number of emitted electrons
What dictates the amount of energy required within a metal to free electrons
The relative position of electrons
Why do electrons on the surface of a metal require the least amount of energy to free
They are subject to few electrostatic forces of attraction to ions
What happens for any given frequency of incident radiation
Only few surface electrons acquire maximum kinetic energy
