Quantum Physics Flashcards
(13 cards)
Define photoelectric effect
THe photoelectric effect is a phenomenon in which electrons are emitted from a metal surface when electromagnetic radiation of sufficient high frequency is incident on the surface
How does the photo tele trick effect occur
Em radiation (uv/visible) strike emitter plate, causing it to emit electrons from it surface. rhe electrons are attracted to the positively charge collector plate c, establishing a photoelectric current
4 observations from experiment
Existence of threshold frequency
Almost immediate emission of photoelectrons
Stopping potential is independent of intensity but dependent on frequency
The photoelectric current produced was proportional to the intensity of the light at constant frequency
define threshold frequency
Threshold wavelength
The lowest frequency that gives rise to ejection of electrons from a particular surface
The highest wavelength that gives rise to ejection of electrons from a particular surface
Define stopping potential
It is the minimum value of potential difference necessary to stop the electron flow
Measured maximum KE of emitted photoelecteons
How does existence of threshold frequency contradict with classical wave theory
Since energy of wave is dependent on square of its amplitude, the classical wave theory predicts that if sufficiently intense light is used, the electrons would absorb enough energy to escape, hence there should not be threshold frequency
How does almost immediate emission of photoelecrrons contradict the classical wave theory
Based on classical wave theory, election should absorb enough energy over a period of time before us gains enough energy to escape the metal
However, photoelectrons were emitted almost immediately even with Low intensity radiation that was above threshold frequency
Why is independent of stopping potential on intensity
According to classical wave theory, by using light with higher intensity, stopping potential should increase as the incident light if higher intensity should eject photoelectrons with a greater KE
But can’t expands why stopping potential is independent of intensity
What is a photon
A photon is a quantum of electromagnetic energy
Define the work function energy of a metal
The work function energy of a metal is defined as the minimum amount of energy necessary for a free electron to escape from the surface if the metal
Define ionisation energy
The ionisation energy of an atom is the minimum energy need to remove an electron completely from the atom
Energy level and line spectra
Lyman (transition to n=4)
Balmer (transition to n=2)
Paschen (transition to n=3)
What is the Heisenberg uncertainty principle
The Heisenberg uncertainty principle states if a measurement of the position of a particle is made with uncertainty delta x and a simultaneous measurement of its component of momentum is made with uncertainty delta p the production of the 2 uncertainties can never be smaller than h/2
