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Concept · Modern Physics
Photoelectric effect & photons
photon energy E=hf=hc/λ, Einstein equation Ekmax=hf-W (work function/threshold frequency), instantaneous emission independent of intensity below threshold, two-wavelength work-function comparisons
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Named traps
11 ways this goes wrong.
Each is a named misconception the questions are built to catch. Open one for the move that tempts, and the fix.
- All photon energy becomes KESets the photoelectron's kinetic energy equal to the full photon energy hf, ignoring the work function spent escaping the metal.→
- E proportional to wavelengthUses photon energy proportional to wavelength rather than to frequency (E=hf=hc/λ).→
- Emission below threshold over timeThinks low-frequency light eventually frees electrons if shone long enough, ignoring the threshold frequency.→
- Intensity equals frequencyConflates light intensity with frequency, treating brighter light as automatically higher-frequency.→
- Intensity raises max KEExpects increasing light intensity to raise the maximum kinetic energy of photoelectrons.→
- Max KE proportional to frequencyTreats Ekmax as directly proportional to frequency, ignoring the subtracted work-function term so a doubled frequency doubles the KE.→
- Photon energy vs intensity confusedBelieves brighter (more intense) light gives each electron more energy, rather than more electrons.→
- Stopping voltage depends on intensityBelieves the stopping potential changes with light intensity rather than with frequency.→
- Two-wavelength work-function errorWhen comparing two illuminating wavelengths on the same metal, treats the work function as changing with wavelength rather than being a fixed property of the metal.→
- Wave theory explains photoeffectMaintains that classical wave theory accounts for the instant, threshold-dependent emission.→
- Work function sign wrongAdds the work function in Einstein's equation (KE=hf+W) instead of subtracting it.→
Key formulas
No formula sheet is matched to this concept yet. Work it from first principles, and watch the traps.
Shaky underneath?
If the concept underneath still feels loose, patch it here before coming back to CSCA questions.
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