# Photoelectric Effect

Overview of photoelectric effect & equations

• Photoelectric Effect
• EM photons allow electrons to be emitted
• Electrons are emitted as long as the light is above the threshold frequency
• High frequency = electrons emit quickly
• Low frequency = electrons emit more slowly
• Ek is independent of light intesity
• Increasing the intensity only increases the amount of photons per second on the area
• Because electrons can only absorb one photon of light at a time
• Work function
• The energy required to break the bonds that hold the electron to the metal
• If energy gained from photon > work function then electrons are emitted
• If energy gained from photon < work function then electrons are not emitted
• f0 = threshold frequency
• Electrons are emitted as long as the light is above the threshold frequency
• High frequency = electrons emit quickly
• Low frequency = electrons emit more slowly
• theta = work function
• h = Planck Constant
• Max kinetic energy
• Energy transferred from EM radiation to electron is the energy it absorbs from one photon
• Photon = hf
• Ek the electron will have when it leaves the metal = hf - other energy losses
• Minimum Ek is the work function energy
• Therefore, max Ek = hf - theta
• Minimum Ek is the work function energy
• Rearrange to give photoelectric equation
• hf = theta + max Ek
• Ek = 1/2mv^2  is max energy a photoelectron can have
• This can be used to write the photoelectric equation as: hf = theta + 1/2mv^2
• hf = theta + max Ek
• Ek = 1/2mv^2  is max energy a photoelectron can have
• This can be used to write the photoelectric equation as: hf = theta + 1/2mv^2
• Stopping potential
• Photoelectrons can be made to lose their energy by doing work against an applied potential difference
• Stopping potential =  pd needed to stop the fastest electrons travelling with max Ek
• eVs = Ek(max)
• where eVs = charge on electron * stopping potential in V