Physics - Quantum (photons)

• h = 6.63x10^-34 (plancks constant)
• E=hf or E=hc/lamda
• c = f x lamda
• Planck theorised that electromagnetic radiation is emitted in discrete packets of energy called quanta
• photon - packets of electromagnetic energy
• The mass of a photon is 0, therefore it travels at the speed of light in a vacuum
• Electronvolt

  1eV is the energy gained by an electron through a p.d of 1V
• eV - Joules = x 1.6x10^-19

  Joules - eV = \ 1.6x10^-19
• V x Lamda = hc/e
• Photons with longer wavelengths have more energy than photons with shorter wavelengths
• The good lead and the plate are given a negative charge by charging the zinc foil. Since the good leaf and the plate have the same charge, they will repel each other, causing the leaf to rise
• When radiating light is shone, electrons are taken out of the gold leaf, discharging it
• Electrons are only released if the frequency of the light illuminating the zinc was carrying a certain frequency, known as the threshold frequency.
• Changing the material of the plate from zinc to different metals changed the threshold frequency required to release electrons
• hf = work function + Kinetic energy (MAX)
• Electrons are emitted if the threshold frequency is greater than the frequency of light
• Work Function


  The minimum energy that photons need to release electrons from the metal
• Photons with a frequency above the threshold frequency cause electrons to be emitted with a range of speeds
• Changing the intensity of a beam of light will change the number of photons emitted per second
• The MAX KE is independent of intensity
• The rate of emission of photoelectrons (above the threshold frequency) is proportional to the intensity
• lamda = h/p = h/mv
• The intensity of a wave at a point represents the probability of a particle being there
• lamda = h/root2xmxKE
• Graphite is a suitable material for the experiment because the spacing between the atoms in graphite is approximately the same as the de Brogile wavelength of the electrons passing through
• momentum (particle) wavelength (wave)
• Wave-particle Duality


  Electromagnetic radiation can display both wave and particle properties; matter can display wave and particle properties
• Photoelectric effect shows waves can behave like particles
• Everyday objects do not show wave-like properties because their de Brogile wavelength is smaller than the size of surrounds. Significant diffraction occurs when the wavelength of the waves is equal the size of the aperture