# Photoelectric Effect. Absorption  Charges can absorb electromagnetic waves. Can cause charge to accelerateCan cause charge to accelerate Moving chargeabsorbed.

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Photoelectric Effect

Absorption  Charges can absorb electromagnetic waves. Can cause charge to accelerateCan cause charge to accelerate Moving chargeabsorbed photon

Ejected Electrons  Electromagnetic energy could eject electrons from the surface. Accelerate with voltageAccelerate with voltage Measure currentMeasure current  Classical expectation is that the current varies with intensity. May also vary with frequency.May also vary with frequency. V e I

Stopping Potential  As the voltage is decreased the photocurrent decreases. Matches classical viewMatches classical view  The voltage can be reversed and some current flows. Stopping point independent of intensityStopping point independent of intensity Characteristic of metalCharacteristic of metal V e I

Atomic View  A photon can eject an electron from an atom. Photon absorbed Electron released  Energy within the atom is quantized. Minimum energy  needed for interaction Einstein’s photoelectric equation e  Z

Work Function  The minimum energy is the work function of the metal.  Below a certain frequency no current can flow. f 0 =  /hf 0 =  /h  Work functions for some metals: Na: 2.28 eV Co: 3.90 eV Al: 4.08 eV Pb: 4.14 eV Zn: 4.31 eV Fe: 4.50 eV Cu: 4.70 eV Ag: 4.73 eV Pt: 6.35 eV

Photocell  The photoelectric effect is commonly used to measure light. Camera light meterCamera light meter  It can also generate electricity. Photovoltaic cellPhotovoltaic cell next

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