1. Physics 3 Photoelectric Effect

2. Photoelectric Effect First observed by Heinrich Hertz in 1887, the phenomenon is also known as the Hertz effect. Hertz observed and then showed that electrodes illuminated with ultraviolet light create electric sparks more easily. 3. Photoelectric Effect The photoelectric effect refers to the emission, or ejection, of electrons from the surface of, generally, a metal in response to incident light. 4. Photelectric Effect In the photoelectric effect, electrons are emitted from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength and high frequency, such as ultraviolet radiation 5. Photelectric Effect Electrons emitted in this manner may be referred to as photoelectrons. The photoelectric effect requires photons with energies from a few electronvolts to over 1 MeV in high atomic number elements. Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of waveparticle duality. 6. Einsteins Equations for the Photoelectric Effect Einstein's interpretation of the photoelectric effect results in equations which are valid for visible and ultraviolet light: energy of photon = energy needed to remove an electron + kinetic energy of the emitted electron h = W + E Where h is Planck's constant is the frequency of the incident photon W is the work function, which is the minimum energy required to remove an electron from the surface of a given metal: h0 E is the maximum kinetic energy of ejected electrons: 1/2 mv2 0 is the threshold frequency for the photoelectric effect m is the rest mass of the ejected electron v is the speed of the ejected electron 7. Einsteins Equations for the Photoelectric Effect No electron will be emitted if the incident photon's energy is less than the work function. 8. In Einsteins model, a photon is localized that it gives all its energy hf to a single electron in the metal. According to Einstein, the maximum kinetic energy for these liberated photoelectrons is Kmax = hf - The freuency is related to the work function through the relationship fc = /h. The cutoff frequency corresponds to a cutoff wavelength of 9. Work Functions of Selected Metals Metal (eV) Na 2.46 Al 4.08 Cu 4.70 Zn 4.31 Ag 4.73 Pt 6.35 Pb 4.14 Fe 4.50