photoelectric effect

Examples of photoelectric effect in the following topics:

• The Photoelectric Effect

  • The photoelectric effect is the propensity of high-energy electromagnetic radiation to eject electrons from a given material.
  • The photoelectric effect has been demonstrated using light with energies from a few electronvolts (eV) to over 1 MeV in high atomic number elements.
  • Study of the photoelectric effect led to an improved understanding of quantum mechanics as well as an appreciation of the wave-particle duality of light.
  • This, in essence, is the photoelectric effect.
  • Kinetic energy must be positive for ejection to take place, so we must have f > f0 for the photoelectric effect to occur.

• Planck's Quantum Theory

  • However, by the early 20th century, physicists discovered that the laws of classical mechanics are not applicable at the atomic scale, and experiments such as the photoelectric effect completely contradicted the laws of classical physics.
  • The wave model cannot account for something known as the photoelectric effect.
  • This effect is observed when light focused on certain metals emits electrons.
  • For each metal, there is a minimum threshold frequency of EM radiation at which the effect will occur.
  • However, in 1905, Albert Einstein reinterpreted Planck's quantum hypothesis and used it to explain the photoelectric effect, in which shining light on certain materials can eject electrons from the material.

• The de Broglie Wavelength

  • This division was challenged when, in his 1905 paper on the photoelectric effect, Albert Einstein postulated that light was emitted and absorbed as localized packets or quanta (now called photons).
  • Therefore, the presence of any diffraction effects by matter demonstrated the wave-like nature of matter.
  • Recent experiments even confirm the de Broglie relations for molecules and macromolecules, which are normally considered too large to undergo quantum mechanical effects.

• Properties of Waves and Light

  • While you will later learn about wave/particle duality (how light behaves as both a wave and a particle at the same time), here we shall discuss the wave nature of light and the experimental effects of this behavior.
  • In the early 19th century, English scientist Thomas Young carried out the famous double-slit experiment (also known as Young's experiment), which demonstrated that a beam of light, when split into two beams and then recombined, will show interference effects that can only be explained by assuming that light is a wavelike disturbance.
  • Almost a century later, in 1905, Albert Einstein's Nobel-Prize winning research into the photoelectric effect demonstrated that light can behave as if it is composed of discrete particles under certain conditions.

• Electromagnetic Spectrum

  • Ultraviolet: Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect).

• The Bohr Model

  • Like Einstein's theory of the photoelectric effect, Bohr's formula assumes that during a quantum jump, a discrete amount of energy is radiated.

• The Shielding Effect and Effective Nuclear Charge

  • The shielding effect, approximated by the effective nuclear charge, is due to inner electrons shielding valence electrons from the nucleus.
  • This effect, called the shielding effect, describes the decrease in attraction between an electron and the nucleus in any atom with more than one electron shell.
  • The magnitude of the shielding effect is difficult to calculate precisely.
  • The term "effective" is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge.
  • What is the effective nuclear charge for each?

• The Common Ion Effect

  • The common ion effect describes the changes that occur with the introduction of ions to a solution containing that same ion.
  • This phenomenon is the common ion effect and plays important roles in pharmaceutical and environmental areas.
  • The common ion effect can be explained by Le Chatelier's principle of chemical equilibrium:
  • Therefore, the common ion effect takes a role in pH regulation.
  • Lithium hydroxide forms less-soluble lithium carbonate, which precipitates because of the common ion effect.

• The Greenhouse Effect

  • The greenhouse effect is an elevation in surface temperatures due to atmospheric gases absorbing and re-radiating thermal energy.
  • The cloud layer can also absorb infrared radiation and contribute further to the greenhouse effect.
  • Without this trapping effect, it is estimated that the surface of the Earth would be approximately 30 degrees cooler than current temperatures.
  • The greenhouse effect modulates the temperature at the Earth's surface and makes it hospitable to life.

• Steric Effects