(2.2) Electromagnetic radiation and quantum phenomena

• What causes beta-minus and beta-plus decay?

  The weak interaction causes a change in quark type
• How does beta-minus decay occur?

  A down quark changes into an up quark in a neutron to turn it into a proton

  
• How does beta-plus decay occur?

  An up quark changes into a down quark in a proton to turn it into a neutron

  
• What is the photoelectric effect?

  Photoelectrons are emitted from a metal surface when light above a certain frequency is shone on it
• Why couldn't the wave theory explain the photoelectric effect?

  The wave theory suggests any frequency of light should cause photoelectric emission, but the photoelectric effect has a threshold frequency
• What is the photon model of light?

  EM waves travel in discrete packets called photons, each with an energy proportional to the frequency
• How does the photon model explain the photoelectric effect?

  Each electron can only absorb a single photon, so photoelectrons are only emitted if the frequency is above the threshold
• What is the work function of a metal?

  The minimum energy required for electrons to be emitted from the surface of a metal
• How can the maximum kinetic energy of photoelectrons be found?

  By measuring the stopping potential, using the equation E_k(max) = e*V_s
• What is the photoelectric equation?

  E = hf = Φ + E_k(max)
• What are the discrete energy levels in atoms?

  Electrons in atoms can only exist in discrete energy levels
• What is excitation and ionisation of electrons in atoms?

  Excitation is when electrons gain energy to move up to a higher energy level, ionisation is when electrons gain enough energy to be removed from the atom entirely

  
• How do fluorescent tubes produce light?

  Electrons accelerated by a high voltage collide with mercury atoms, exciting them, and when the mercury atoms de-excite they emit UV photons which are absorbed by the fluorescent coating and re-emitted as visible light

  
• What is an electron volt (eV)?

  The energy gained by one electron when passing through a potential difference of 1 volt
• How do you convert between eV and J?

  To convert from eV to J, multiply by 1.6x10^-19, and to convert from J to eV, divide by 1.6x10^-19
• What is a line spectrum?

  A spectrum containing only discrete wavelengths of light, rather than a continuous spectrum
• How does a line absorption spectrum differ from a line emission spectrum?

  A line absorption spectrum has dark lines at certain wavelengths in an otherwise continuous spectrum, while a line emission spectrum has bright lines at certain wavelengths
• What is the relationship between the energy difference of two levels and the frequency of emitted/absorbed photons?

  The energy difference ΔE between two levels is equal to the energy of the emitted/absorbed photon, which is given by E = hf
• What is wave-particle duality?

  Light and matter (e.g. electrons) can exhibit both wave-like and particle-like properties
• How does the De Broglie equation relate the wavelength of a particle to its momentum?

  The wavelength λ of a particle is inversely proportional to its momentum p, given by λ = h/p
• How did the scientific community's understanding of wave-particle duality evolve over time?

  Scientists initially did not agree that matter had wave-particle duality, but as experimental evidence like electron diffraction accumulated, it was eventually accepted
• What are the key differences between beta-minus and beta-plus decay?

  • Beta-minus decay: A down quark changes into an up quark in a neutron, turning it into a proton
  • Beta-plus decay: An up quark changes into a down quark in a proton, turning it into a neutron
• How does the photon model explain the photoelectric effect?

  • EM waves travel in discrete packets called photons
  • Each electron can only absorb a single photon
  • Photoelectrons are only emitted if the photon energy (frequency) is above the work function
  • Increasing light intensity increases the number of photoelectrons emitted, not their energy
• How do fluorescent tubes produce visible light?

  • Electrons accelerated by a high voltage collide with mercury atoms, exciting them
  • The excited mercury atoms then de-excite, emitting UV photons
  • The UV photons are absorbed by the fluorescent coating, which then re-emits visible light photons

  
• How do line emission and absorption spectra differ?

  • Line emission spectrum: Discrete bright lines on a dark background
  • Line absorption spectrum: Dark lines on an otherwise continuous spectrum
  • Both indicate that atoms can only absorb/emit photons with specific energies corresponding to transitions between discrete energy levels
• How can the De Broglie equation be used to understand electron diffraction?

  • The De Broglie equation relates the wavelength λ of a particle to its momentum p: λ = h/p
  • As the momentum of an electron increases, its wavelength decreases
  • This change in wavelength affects the amount of diffraction observed, with higher momentum electrons showing less diffraction
• How did the scientific community's understanding of wave-particle duality evolve over time?

  • Initially, scientists did not agree that matter had wave-particle duality
  • As experimental evidence like electron diffraction accumulated, the wave-particle duality of matter was eventually accepted
  • Scientific knowledge and understanding evolves as new experimental evidence is gathered and validated by the scientific community