I Introduction In 1901 Max Karl Ernst Ludwig Planck published his revolutionary In equation form, it is E=nhv where E and v are the energy and frequency of an oscillator in the solid; n is a positive integer. The constant h=6.626x 10-34 J-s is Planck's constant. For this innovation Planck was awarded the Nobel Prize in 1918. the citation for which reads in recognition of the services he rendered to the advancement of Physics by his discovery of energy quant Equation 1.1, the Planck relation, is often written in terms of the angular fre- quency a= 2v and h= h/2. The symbol h is read"h-bar"and E=nho Einsteins explanation of the photoelectric effect rested on Plancks assumption that Equation 1. I also applied to light emitted by the oscillators. As a consequence, it was inferred that light(electromagnetic radiation) could be considered to be made up of bundles or"quanta"called photons, each having energy E and frequency v. Thus was born the concept of wave particle duality. That is, light exhibits both particle properties, quanta having energy E, and wave properties as represented by the frequency v. It is common to speak of light in terms of the wavelength a rather han the frequency, in which case Equation 1. I takes the form λ where c is the speed of light Now, what are the details of the photoelectric effect? The observations are best understood in terms of the experiments. A schematic diagram of the apparatus used by Lenard, and later Milliken, is shown in Fig. 1.la Light of a fixed frequency(monochromatic light)illuminates an elemental metal, the photocathode. Electrons are emitted from the photocathode, collected on the v=constant Fig 1.1 (a) Schematic iagram of the apparatus used n the photoelectric effect. The photocathode and anode are labeled PC and A resp light of frequency hv (b) Simulated data2 1 Introduction In 1901 Max Karl Ernst Ludwig Planck published his revolutionary hypothesis. In equation form, it is E = nhν (1.1) where E and ν are the energy and frequency of an oscillator in the solid; n is a positive integer. The constant h = 6.626 × 10−34 J·s is Planck’s constant. For this innovation Planck was awarded the Nobel Prize in 1918, the citation for which reads “in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta”. Equation 1.1, the Planck relation, is often written in terms of the angular fre￾quency ω = 2πν and = h/2π. The symbol is read “h-bar” and E = nω (1.2) Einstein’s explanation of the photoelectric effect rested on Planck’s assumption that Equation 1.1 also applied to light emitted by the oscillators. As a consequence, it was inferred that light (electromagnetic radiation) could be considered to be made up of bundles or “quanta” called photons, each having energy E and frequency ν. Thus was born the concept of wave particle duality. That is, light exhibits both particle properties, quanta having energy E, and wave properties as represented by the frequency ν. It is common to speak of light in terms of the wavelength λ rather than the frequency, in which case Equation 1.1 takes the form E = hc λ (1.3) where c is the speed of light. Now, what are the details of the photoelectric effect? The observations are best understood in terms of the experiments. A schematic diagram of the apparatus used by Lenard, and later Milliken, is shown in Fig. 1.1a. Light of a fixed frequency (monochromatic light) illuminates an elemental metal, the photocathode. Electrons are emitted from the photocathode, collected on the Fig. 1.1 (a) Schematic diagram of the apparatus used in the photoelectric effect. The photocathode and anode are labeled PC and A, respectively. Monochromatic light of frequency hν illuminates the photocathode. (b) Simulated data