The Photoelectric Effect
BlackBoard Notes

  ======================= Photo - Click for a Larger Version =============================

Note to Jeff: Substitutue φ_w for W; need new photo 2026

======================= First Board Section =============================

• What affects the energy of electrons ejected from a metal surface: the intensity of light {wave theory} or frequency/color {photon theory}?
• Inside the photoelectric head:

• Electrons ( e^– ) absorb energy and can be ejected

======================= Second Board Section =============================

• Photon Model:
  • Photons carry energy: E = hf
    • (Point to parts of first equation and label that K is kinetic energy, φ_w is e^– binding energy; see blackboard photo for tips)

(Where φ_w ⇒ electron binding energy; h ≡ Planck's constant)

======================= Third Board Section =============================

• Kaleidagraph: Plot eV_stop vs. f  

• Create custom fit in Kaleidagraph
  • Refer to "Finding the Best-Fit Function"
• Calculate h & φ_w (and their uncertainties).
• Units – electron-volt (eV): Amount of K gained (or lost) by an electron accelerating through an electric potential difference of 1 volts.
  • If V = 5 volts, what is K?

======================= Fourth Board Section =============================

• Wave theory:
  • K_max depends on light intensity (brighter light → greater ejected energy)
  • Use "Relative transmission" slide
    • Regions with 20%, 40%, 60%, 80% and 100% transmission
• Notes:
  • Use yellow and green filters for yellow and green lines only!!
  • The mercury lamp is HOT!
  • Don't turn off Hg lamp until you are finished with lab.
  • Do turn off multimeter & flashlight!

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©	St. Lawrence University	Department of Physics

Revised: 10 Apr 2026

Canton, NY 13617