Quantum Physics

• The order of the electromagnetic spectrum is: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays.
• Radio waves are the highest wavelength and lowest frequency waves therefore the lowest energy also. They have a wavelength around 10$^3$
• Radio waves for communication such as broadcasting television and satellite transmissions.
• Microwaves are high wavelength low frequency waves with little energy. They have a wavelength around 10$^{-2}$ m
• Microwaves are used for cooking and satellite communications.
• Infrared radiation have wavelengths around 10$^{-5}$m.
• Infrared radiation is used for electrical heaters, short range communications and thermal imaging
• Visible light is in the middle of the spectrum and has a wavelength around 10$^{-6}$m
• Visible light is used in photography and illumination.
• Ultraviolet light has a wavelength of around 10$^{-8}$m
• Ultraviolet light is used to sterilise water and food, to detect forgeries of bank notes and in energy efficient light bulbs.
• X-rays are low wave length and high frequency with high energy. They have wavelength of around 10$^{-10}$ m
• X-rays are used to diagnose and treat diseases, such as cancer and also for internal imaging
• Gamma rays are the lowest wavelength and highest frequency waves with the highest energy. They have a wavelength of around 10$^{-12}$m
• Gamma rays are used for sterilising food and medical instruments as well as in the treatment and detection of cancer
• A photon is a quantum of electromagnetic energy. 


  E = h f and c = f$\lambda$

  E = $\frac{hc}{\lambda}$ which gives the equation for photon energy in terms of wavelength
• Photon energy is directly proportional to their frequency
• Photon energy is inversely proportional to their wavelength
• The photoelectric effect occurs when light is above a particular frequency is incident on a metal surface, causing electrons to be emitted from the surface.

  
• In the photoelectric effect, photoelectrons are only emitted if the incident light is above a particular frequency known as the threshold frequency.
• In the photoelectric effect, the maximum kinetic energy of the emitted electrons does not change when the intensity of the incident light is increased. Instead, the number of electrons emitted increases.
• In the photoelectric effect, increasing the frequency of incident light increases the maximum kinetic energy of the photoelectrons emitted
• In the photoelectric effect, there is a one-to-one interaction between photons and electrons which means one photon causes the emission of one photoelectron
• The photoelectric effect provides evidence that contradicts the wave theory of light and provides evidence for the particle nature of light.
• Each photon has energy which is proportional to the frequency of light therefore the energy of a particle is:


  E = h f
• The lowest frequency of light that causes electrons to be emitted is known as the threshold frequency.
• The work function is the minimum energy needed to remove an electron from the surface of a metal.


  f$_0$ = $\frac{\Phi}{h}$
• To calculate the kinetic energy of the photoelectrons emitted from the photoelectric effect:


  E = hf = $\Phi$ + KE$_{max}$
• The energy of 1eV is defined as the energy transferred to or from an electron when it moves through a potential difference of 1V


  The work done on an electron is equal to: W = $e$V where e =1.6 x 10$^{-19}$
• Light exhibits both wave and particle properties. Therefore momentum of the photon can be related to wavelength


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