photoelectric effect

• Photoelectric Effect


  The phenomenon where electrons are emitted from a metal surface when exposed to light of sufficient frequency
• The Photoelectric Effect Couldn't be Explained by Wave Theory
• Wave Theory Explanation

  1. Energy proportional to intensity

  2. Energy spread evenly

  3. Electrons gain energy from waves

  4. Electrons leave metal
• The higher the intensity of the wave, the more energy it should transfer to each electron
• There’s no explanation for the kinetic energy depending only on the frequency
• There is also no explanation for the threshold frequency
• Shining Light on a Metal


  1. Free electrons absorb energy

  2. Electrons break bonds and are released

  3. This is called the photoelectric effect
• For most metals, the frequency falls in the UV range
• Intensity

  The power hitting a given area of the metal
• what is happening?


  a mobile electron absorbs a uv photon giving it enough energy to escape the surface of the metal

  
• phtotelectrons are emitted from the surface of the metal and travel through the air they are like normal electrons
• photoelectrons are released by uv light above the threshold frequency(fmin)
• fmin depends on type of metal
• number of photoelectron released per second is proportional to the intensity of the light source
• photoelectrons are released instantly when exposed to uv light with f > fmin
• what is work function?

  Minimum energy required to remove an electron from a metal given in eV
• threshold frequency is the minimum frequency to overcome work function and allow electrons to pass through the surface
• photoelectric effect id proof that EM radiation act like particles and not waves
• intensity of wave doesn't affect the emission of electrons from the surface of a metal, only the frequency of the wave
• the only factor that affects the energy received by the electron is photon energy (E=hf)
• higher frequency = more energy photon so more energy the photons receives = greater speed of photoelectric effect
• threshold frequency is when work function =hf
• when above the threshold frequency thats when intensity affects the emissions it affects the distance the electrons travel, energy will go to ke of emitted electrons
• photoelectric equation

  E=hf= work function + 1/2 mv^2( ke)
• stopping potential is the potential difference needed to stop electrons (Vs)
• Ekmax =eVs

  Ekmax is max ek of photoelectrons

  Vs is stopping potential

  e is 1.6x10^-19C
• stoping potential equation

  E=hf=work function+eVs
• Ekmax = hf

  gradient=h

  
• intensity of light = nhf/T
• number of photons = power(nhf)/hf