Quantum Phenomena Flashcards
Photoelectric effect
If shine light of high enough frequency on to surface of a metal an electron absorbs enough energy for bonds to break releasing a photo electron
Work function
Minimum energy required for the electron to be emitted
3 main conclusions of photoelectric effect
For a given metal, no photoelectrons emitted if radiation has frequency lower than certain value
Photoelectrons are emitted with variety of kinetic energies ranging from 0 to Max value, max value increases with frequency of radiation
Number of photoelectrons emitted per second proportional to intensity of radiation
Excitation
Movement of an electron to a higher energy level
Ionisation energy
Amount of energy needed to completely remove an electron from the atom from the ground state
Fluorescent tubes
Contain mercury vapour across with initial high voltage applied. High voltage accelerates fast moving free electrons that ionise some of the mercury atoms producing more free electrons
When flow of free electrons collided with electrons in other mercury atoms the electron in mercury become excited
Excited return to ground emitting photon in uv range
Phosphorus coating absorbs photons exciting it’s electrons which then cascade down energy level emitting many lower energy photons in visible light
Threshold frequency
The minimum frequency required for a photo electron to be emitted
Stopping potential
Idea by which maximum kinetic energy can be measured
eVs=Ek(max)
eV
Kinetic energy carried by an electron after it has been accelerated through a potential difference of 1 volt
What did De Broglie suggest
If wave like light shower particle properties, particles like electrons should be expected to show wave like properties
How are diffraction patterns observed
Observed when accelerated electrons in a vacuum tube interact with spaces in graphite crystal
What does electron diffraction show
Smaller accelerating voltage of electrons gives wider rings
How does electron diffraction link to de Broglies wavelength
Increase electron speed and the diffraction pattern circles squash together towards the middle. Fits equation as if momentum is greater the wavelength is shorty and spread of lines is smaller
What is needed for electron diffraction
Only get diffraction if a particle interacts with an object of about the same size as it’s de Broglie wavelength
