Optical Phenomena
Photoelectric effect, emission spectra
The Photoelectric Effect
The photoelectric effect occurs when light ejects electrons from a metal surface. Einstein: light consists of photons with energy E = hf. Electrons are ejected only if photon energy exceeds the work function: Ek(max) = hf - W0.
Example
Worked Example
Metal work function: 4.5 x 10 to -19 J. UV light frequency: 8 x 10 to 14 Hz. E_photon = hf = (6.63 x 10 to -34)(8 x 10 to 14) = 5.3 x 10 to -19 J. Since E > W0, electrons ejected. Ek(max) = 0.8 x 10 to -19 J.
Note
Exam Tip
The photoelectric effect supports the particle nature of light. Threshold frequency f0: W0 = hf0. Increasing intensity increases the number of electrons ejected, not their maximum kinetic energy.
Key Vocabulary
Photoelectric effectEmission of electrons from a metal when light of sufficient frequency shines on it
PhotonA packet (quantum) of light energy
Work functionThe minimum energy needed to eject an electron from a metal surface
SASL Avatar
Loading avatar...
1 / 3
Photoelectric effect
Speed: