Chapter 13

• A photon is a quantum of electromagnetic energy.
• The energy of a photon is determined by


  $E=$$hf$$E=$$\frac{hc}{\lambda}$
• Planks constant is $6.63\times10^{-34}$
• The energy of a photon is inversely proportional to wavelength


  $E\propto\frac{1}{\lambda}$
• Electronvolts is the energy transferred to or from an electron when it moves through a potential difference of 1V
• Energy of photons is measured in joules and electronvolts (eV). To convert between them you divide by$1.6\times1-^{-19}$
• Energy of photons is measured in joules and electronvolts (eV). To convert between them you divide by $1.6\times10^{-19}$
• Planks constant can be investigated using LED's. The minium potential difference required to turn on the LED, threshold p.d., is recorded. At the threshold p.d. the energy transferred by and electron is approximately equal to the energy a photon emits. This is used to plot a graph of voltage against $\frac{1}{\lambda}$. h can be calculated from the gradient of the line (gradient $=$$\frac{hc}{e}$
• The photoelectric effect is the emission of electrons from a metal surface when light is shone on it
• The photoelectric effect can be investigated using a gold-leaf electroscope. UV light is shone onto a charged zinc plate with a thin gold leaf on top which is also charged. The leaf collapses whish shows that electrons were emitted from the metals surface
• From the photoelectric effect we can observe that photoelectrons are only emitted if the incident radiation is above the threshold frequency. If this is true, photoelectrons are emitted instantaneously and increasing the intensity of the incident radiation has no effect on the maximum kinetic energy of the photoelectrons. Instead more photoelectrons were emitted.
• How does the photoelectric effect work?

  Each surface electron requires a certain amount of energy to escape the metal.Each photon in the incident radiation transfers the exact energy to the electron in a ONE ON ONE interactionEnergy of the photon is dependent on wavelength therefore the photons must have sufficient frequency to release photoelectronsTherefore if the energy of the photons is below the threshold frequency, increases in intensity will make no difference
• The photoelectric effect effect equation

  $hf=$$\Phi+$$KE_{max}$
• Wave particle duality is a model used to describe how matter can have both wave and particle properties
• Electron diffraction can be demonstrated using an electron gun. It's used to fire electrons at a thin piece of polycrystalline graphite. The gaps between the carbon atoms are similar to the wavelength of the electrons so the electrons diffract. A sensor and screen is used to create an interference pattern
• Wavelength is inversely proportional to momentum


  $\lambda=$$\frac{h}{mv}$