الفيزياء: الكترونات وخصائصها

Electromagnetic Waves

• Electromagnetic radiation is a form of energy stored in both electric and magnetic fields.

• Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation.

• The speed of electromagnetic waves is equal to the speed of light.

• Electromagnetic waves are not affected by electric and magnetic fields.

• Electromagnetic waves can be reflected, refracted, interfered, diffracted, and polarized.

• The ability of a body to emit visible or invisible radiation is a thermal property.

• The emissivity of a body is proportional to its absorptivity.

• A good absorber of radiation is also a good emitter of radiation.

• A blackbody is a perfect absorber and emitter of radiation.

• The energy radiated from a blackbody is given by:

  • λλεαλ
  • Energy emitted per unit area per unit wavelengths range
  • Measured in W/m²

• The speed of electromagnetic waves in a vacuum is given by:

  • c = 1/√(μ₀ε₀)
  • Where:
    • μ₀ is the magnetic permeability
    • ε₀ is the permittivity

Photoelectric Effect

• Electrons are emitted from a metal surface when light shines on it. This phenomenon is called the photoelectric effect.
• The kinetic energy of emitted electrons does not depend on the intensity of the incident light, but on the frequency of the light.
• The number of emitted electrons increases with the intensity of the incident light.
• The metal surface absorbs light in discrete units called quanta or photons.
• Light can be considered as composed of photons that travel at the speed of light.

Einstein Equation for Photoelectric Effect

• The maximum kinetic energy of emitted electrons is equal to the energy of the incident photons minus the work function of the metal.
• Ek_max = hv - Φ
• Where:
  • Ek_max is the maximum kinetic energy of the emitted electrons.
  • h is Planck's constant.
  • v is the frequency of the incident light.
  • Φ is the work function of the metal.

X-rays

• X-rays travel in straight lines.
• X-rays are uncharged, so they are not affected by electric or magnetic fields.
• X-rays have wave nature.
• X-rays are transverse waves.
• X-rays are electromagnetic waves (similar to visible light), but their wavelengths are much shorter.

X-ray Spectra

• Continuous spectrum: emitted when fast electrons interact with the target. The emitted X-ray photons can have any energy up to the initial kinetic energy of the electron.
• Line spectrum: emitted when fast electrons cause electron transitions in inner energy levels of atoms, producing specific energies and wavelengths. The transitions between specific energy levels relate to the atoms involved (the target).

Bohr's Postulates for the Atom

• Electrons orbit the nucleus in circular paths under the influence of the Coulomb force.
• Certain orbits are stable, in which electrons do not emit radiation, and thus have constant energy.
• Radiation is emitted when an electron transitions from a higher energy orbit to a lower energy.
• The allowed orbits for the electron are determined by a quantized condition.

De Broglie's Hypothesis

• Electrons exhibit wave-like properties. Thus, each electron is associated with a wave.
• The wavelength of the electron is inversely proportional to its momentum. - λ = h/p - Where: - λ is the wavelength of the electron. - h is Planck's constant. - p is the momentum of the electron.

Atomic Models (Isotopes, Isotones, Isobars, Isomers)

• These are related to different forms of the same nuclei.

Physics Laws of Conservation

• Law of conservation of mass
• Law of conservation of energy
• Law of conservation of momentum
• Law of conservation of angular momentum
• Law of conservation of charge

Classical Physics vs. Relativity

• Classical physics (Newtonian) describes objects moving at normal speeds (not near the speed of light).
• Relativistic physics describes objects moving at speeds close to the speed of light.

X-ray Production

• X-rays are produced when high-speed electrons interact with a target material. An X-ray tube contains a cathode (electron source), an anode (target), and a high voltage source.
• Continuous spectrum: produced by bremsstrahlung (deceleration) of electrons as they interact with the nucleus of atoms.
• Characteristic spectrum: produced by electron transitions between energy levels in the atoms of the target material. The emitted X-ray photons have specific energies and thus specific wavelengths.

X-Ray Applications

• Crystallography: X-ray diffraction patterns are used to determine the structure of crystals.
• Medicine: medical imaging (X-ray imaging).
• Security: airport security screening.
• Industry: quality control of materials.
• Art: Authenticating historical artifacts.

X-ray Hazards and Safety

• X-ray exposure can be harmful to living tissue. The risk increases with cumulative exposure.

Uncertainty Principle

• It is impossible to simultaneously determine both the position and momentum of a particle with perfect accuracy.
• ΔxΔp ≥ h/4π
• Where:
  • Δx is the uncertainty in position.
  • Δp is the uncertainty in momentum.
  • h is Planck's constant.

Line Spectra

• Line spectra are the discrete lines seen in the spectra of atoms.
• The lines arise from electronic transitions between different energy levels (quantum jumps) in the atom as it emits or absorbs radiation.
• Different elements have unique line spectra, making them valuable for identifying substances.

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