Chapter 3 - Quantum phenomena Flashcards
What is the photoelectric effect?
The emission of electrons from a metal surface when electromagnetic radiation above a certain frequency (threshold frequency) is directed at the surface.
What are photoelectrons?
The electrons emitted by the photoelectric effect.
What is the threshold frequency?
The minimum frequency of light that can cause photoelectric emission.
What is the work function (ϕ) of a metal?
The minimum energy needed by an electron to escape from its surface.
What is the stopping potential?
The minimum potential needed to stop photoelectric emission from a metal.
What is Ek(max)?
The maximum possible kinetic energy of the photoelectrons.
What is ionisation?
Any process of creating ions.
What is 1 eV in joules?
1.60 x 10 -19J
What is an electron volt?
The unit of energy which is defined as equal to the work done when an electron is moved through a potential difference of 1 V.
What is excitation?
The process in which gas atoms absorb energy from colliding electrons without being ionised.
In this process, the free colliding electron makes an electron inside the atom move from an inner shell to a higher shell.
What experiment suggest that particles possess wave properties?
Electron diffraction
Momentum (particle property) is shown to affect the wavelength (wave property) of electrons and thus the spread of lines on a diffraction pattern.
What experiment suggests that electromagnetic waves have a particulate nature?
Photoelectric effect
It cannot be explained by wave theory but it can be explained by Einstein’s photon model of light.
The number of electrons emitted per second by a metal surface is proportional to the ______ of the incident radiation.
The number of electrons emitted per second by a metal surface is proportional to the intensity of the incident radiation.
Explain how a fluorescent tube works.
Fluorescent tubes contain mercury vapor, across which an initial high voltage is applied which accelerates free electrons through the tube.
When this flow of free electrons collides with electrons in mercury atoms, the electrons in the mercury atoms are excited to higher energy levels.
When these excited electrons return to their ground states, they emit photons in the UV range.
The coating inside the tube absorbs these photons, exciting the electrons to much higher orbits. These electrons then cascade down the energy levels, emitting many lower energy photons in the form of visible light.
