Quantum Mechanics & the Nature of Matter, Motion and Reality

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Presentation transcript:

Quantum Mechanics & the Nature of Matter, Motion and Reality

The Photoelectric Effect

The Photoelectric Effect

The Photoelectric Effect Shining light on metal causes the “photo-emission” of energetic electrons.

The Photoelectric Effect Lag time Light Intensity. Altering light intensity has no effect on lag time of electron emission. It is always instantaneous!!

The Photoelectric Effect Lag time Threshold frequency Light freq. Altering light frequency reveals a “threshold frequency” below which the photoemission of electrons does not take place.

The Photoelectric Effect Sample Threshold Frequencies Aluminum: 0.985 x1015 Hz Lead: 0.999 x1015 Hz Zinc: 1.038 x1015 Hz Iron: 1.086 x1015 Hz Copper: 1.134 x1015 Hz Silver: 1.141 x1015 Hz Nickel: 1.209 x1015 Hz Gold: 1.231 x1015 Hz Platinum: 1.532 x1015 Hz fth Higher threshold frequency requires “bluer” light to cause photo-emission. Most threshold frequencies lay in the UV spectrum. Heating a metal can change threshold frequency by increasing electron energy.

The Photoelectric Effect Lag time Threshold frequency Light freq. Altering light frequency reveals a “threshold frequency” below which the photoemission of electrons does not take place.

The Photoelectric Effect KE Light freq. At higher frequencies the ejected electrons are more energetic.

The Photoelectric Effect KE Light intensity. Changing the brightness of the light has no effect on the energy of ejected electrons.

The Photoelectric Effect Light intensity. Changing the brightness of the light does affect the number of ejected electrons.

The Photoelectric Effect Light intensity. Energy of light is quantized into discrete energy ‘bundles’ called… photons KE Light freq.

The Photoelectric Effect Light intensity. Energy of light is quantized into discrete energy ‘bundles’ called photons. Intensity  # photons KE Light freq.

The Photoelectric Effect Light intensity. Energy of light is quantized into discrete energy ‘bundles’ called photons. Intensity  # photons Freq.  photon energy KE Light freq.

The Photoelectric Effect Light intensity. Energy of light is quantized into discrete energy ‘bundles’ called photons. Intensity  # photons Freq.  photon energy KE e = hf Light freq.

The Photoelectric Effect photon energy  electron kinetic energy + extra KE = ½ mv2 e = hf

The Photoelectric Effect photon energy  electron kinetic energy + extra hf  ½ mv2 + f KE = ½ mv2 e = hf

The Photoelectric Effect photon energy  electron kinetic energy + extra hf  ½ mv2 + f e  KE + f KE = ½ mv2 e = hf

The Photoelectric Effect photon energy  electron kinetic energy + extra hf  ½ mv2 + f e  KE + f e = KE + f KE = ½ mv2 e = hf

The Photoelectric Effect photon energy  electron kinetic energy + extra hf  ½ mv2 + f e  KE + f e = KE + f KE = ½ mv2 e = hf

The Photoelectric Effect Sample Work Functions Aluminum: 6.531 x10-19 J Lead: 6.623 x10-19 J Zinc: 6.882 x10-19 J Iron: 7.200 x10-19 J Copper: 7.518 x10-19 J Silver: 7.565 x10-19 J Nickel: 8.016 x10-19 J Gold: 8.162 x10-19 J Platinum: 10.16 x10-19 J f Different metals have different work functions. The work function of a metal “subtracts” energy away from incoming photons. Heating a metal can change the metal’s work function.

The Photoelectric Effect Sample Work Functions Aluminum: 4.08 eV Lead: 4.14 eV Zinc: 4.30 eV Iron: 4.50 eV Copper: 4.70 eV Silver: 4.73 eV Nickel: 5.01 eV Gold: 5.10 eV Platinum: 6.35 eV f Different metals have different work functions. The work function of a metal “subtracts” energy away from incoming photons. Heating a metal can change the metal’s work function.

E = Q/4peor² B = moI/2pr But I modeled light as a wave!? Energy of light is quantized into discrete energy ‘bundles’ called… photons But I modeled light as a wave!?

Planck Equation : e = hf Enet = ne e = KE + f Planck-Einstein