Contact person: A.Frenkel

Location: Beamline X16C, National Synchrotron Light Source (NSLS)

Description:  

The Nobel Prize in Physics 1921 was awarded to Albert Einstein "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect"

Citing the article published in Nobel e-Museum, in 1905, Albert Einstein was working as a clerk at the Swiss Patent Office in Bern. He was completely unknown in the physics community. This was about to change as he published three seminal papers in a single journal volume during that year. As well as explaining the photoelectric effect, he also sought to prove the existence of atoms and introduced relativity. Not bad for a 26-year old!

Heinrich Hertz first observed the photoelectric effect in 1887. This was one of those handful of phenomena that Classical Physics could not explain. Hertz had observed that, under the right conditions, when light is shined on a metal, electrons are released and produce the electric current (the photo-current).. Among other surprising properties of the newly discovered effect,  particularly troubling was the effect observed by Lenard, when the wavelength and intensity of the light which struck the surface were changed. The photocurrent did change proportionally to the  incident light intensity! 

To explain the photoelectric effect, Einstein reasoned that if the energy of oscillators was quantied as demonstrated by Planck, then the energy of electromagnetic fields (i.e.: light) could be given the same treatment. Up to this point, all phenomena involving light (such as diffraction) was explained in terms of waves. Now, Einstein's treatment meant the light could arrive in discrete packets - which he dubbed photons. Light now had a dual nature. Depending on the experiment, light behaved as either a particle or a wave!

At Brookhaven, students will explore the photoelectric effect by studying photo-ionization of gases in modern x-ray detectors called ionization chambers. Students will reproduce the discovery of Lenard (that doubling light intensity doubles the photocurrent but does not alter the emitted electrons energy). They will use K-edges of Ar, Kr and Xe gases to obtain the work functions of their K-electrons.