QUANTUM PHENOMENA---A level physics proper revision

Quantum Phenomena

• PHOTOELECTRIC EFFECT
• Shows that light can behave as a particle and as a wave.
• Can only be explained with regards to light acting as particles or quanta of energy
• WORK FUNCTION is the MINIMUM energy required to RELEASE AN ELECTRON from surface of metal, varies depending on metal. [Therefore the Threshold Frequence is dpendent on the type of metal used.]
• THRESHOLD FREQUENCY is the MINIMUM frequency for electrons to overcome the work function
• No photoelectric emission of electrons from a metal surface if the frequency is below the threshold frequency.
• -This is because the energy of a photon depends on the frequency. E=hf
• -Below the threshold frequency, the photon does not have enough energy to liberate the electrons [IN TERMS OF WF]
• -OR, photon does not have enough energy to allow the electron to overcome the work function. [IN TERMS OF TF]

Folie 2

• According to C=fλ, the wavelength of light must be below a maximum value. ASK!
• Maximum KE of electrons increases with frequency-unaffected by intensity.
• Higher intensity= More photons, so more electrons are emitted- proportional.
• Electrons absorb 1 photon at a time- 1 to 1 Interaction.
• Frequency affects electron ENERGY, intensity affects NUMBER of electrons emitted.
• There is no time delay unlike predicted:
• Light travels as photons
• Which carry energy in discrete packets
• With 1 to 1 interaction
• Emitted electrons have a range of Kinetic Energies up to a maximum because:
• -Energy of Photons is fixed/constant
• -1-1 interaction between photon and electron
• -Energy=req for electron to escape from the metal surface
• -Electron needs to overcome work function
• -Max KE= PHOTON ENERGY-WORK FUNCTION
• -more energy=req to remove deeper electrons, so they have less KE.

Explan-PE effect- The photon model of light

• Energy of each photon--> E=hf
• When light is incident on a metal surface, and electron at the surface absorbs a single photon from the incident light and therefore gains energy equal to hf (1:1 interaction).
• Work Function (ϕ)= minimum energy needed for an electron to be emitted- energy needed to break the bonds holding it in place.
• Threshold Frequency= Minimum frequency needed for an electron to overcome work function and be emitted.
• Below this, no electrons are emitted. stands for small letters-->[X]
• E=hf. H=constant. Therefore frequency determines Energy.
• Therefore threshold frequency determines work function.
• Therefore ϕ=hXf[thresh] (h=planck's constant: 6.63x10^-34)
• Work function of a metal is related to the Threshold Frequency (f[min])
• f[min]= ϕ/h