Physics Chapter: Dual Nature of Radiation and Matter

Dual Nature of Radiation and Matter

• Dual nature : Matter and radiation exhibit both wave-like and particle-like properties.
• Electron Emission : Electrons can be emitted from a material through different methods:
  • Thermionic emission: Through heat
  • Field emission: Strong electric fields
  • Photoelectric emission: Light of a certain frequency
• Photoelectric effect: Light striking a material causes emission of electrons.
  • Key concept: The maximum kinetic energy of emitted electrons depends on the frequency of the incident light and the work function of the material. It does not depend on the intensity of incident light.
  • Einstein's Photoelectric equation: KE_max = hν - Φ₀, where KE_max is maximum kinetic energy, h is Planck's constant, ν is frequency, and Φ₀ is the work function.
  • Threshold frequency: Minimum frequency needed to cause emission.
  • Threshold wavelength (λ₀): Maximum wavelength that causes emission.
• Wave nature of matter (De Broglie wavelength) : Matter possesses wave-like properties.
  • De Broglie wavelength: λ = h/p, where h is Planck's constant and p is momentum.
  • De Broglie wavelength is inversely proportional to momentum.
• Davisson-Germer experiment: Provided experimental verification of matter waves, demonstrating electron diffraction.

Photoelectric Effect

• Photons: Energy packets of electromagnetic radiation
  • Energy of a photon: E = hν = hc/λ , where h is Planck's constant, c is the speed of light and λ is wavelength.
• Momentum of a photon: p = E/c = h/λ
• Relationship between frequency and wavelength: ν=c/λ
• Important constants: h = 6.626 x 10^-34 Js, c = 3 x 10⁸ m/s
• Experimental observations of photoelectric effect:
• The kinetic energy of emitted electrons depends on the frequency of the incident light.
• There is zero time lag between the incidence of the light and the emission of electrons.
• Electrons are emitted only when the frequency of light is greater than the threshold frequency.