1. Quantum Mechanics & the Nature of Matter, Motion and Reality

2. The Photoelectric Effect

3. The Photoelectric Effect

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

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

6. 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.

7. The Photoelectric Effect
Sample Threshold Frequencies
Aluminum: x1015 Hz Lead: x1015 Hz Zinc: x1015 Hz Iron: x1015 Hz Copper: x1015 Hz Silver: x1015 Hz Nickel: x1015 Hz Gold: x1015 Hz Platinum: 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.

8. 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.

9. The Photoelectric EffectKE
Light freq.
At higher frequencies the ejected electrons are more energetic.

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

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

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

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

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

15. 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.

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

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

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

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

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

21. The Photoelectric Effect
Sample Work Functions
Aluminum: x10-19 J Lead: x10-19 J Zinc: x10-19 J Iron: x10-19 J Copper: x10-19 J Silver: x10-19 J
Nickel: x10-19 J Gold: x10-19 J Platinum: 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.

22. The Photoelectric Effect
Sample Work Functions
Aluminum: eV Lead: eV Zinc: eV Iron: eV Copper: eV Silver: eV
Nickel: eV Gold: eV Platinum: 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.

23. 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!?

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