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Phys205L DETERMINATION OF PLANCK’S CONSTANT 1. Object : To determine Planck’s constant by means of the photo-electric effect. 2. Equipment : Mercury vapor light source, digital voltmeter, Lens/Grating assembly, PASCO h/e apparatus, green and yellow filters. 3. Theory : The photoelectric effect is a process in which light incident on a metal surface (usually a cathode in a vacuum tube) can cause electrons to be ejected from that surface. According to the quantum theory of light that was introduced by Max Planck in 1901, the energy, E, of a photon is given by: E=h ν (1) Where is the frequency of the radiation and h is Planck’s constant, which is the constant of proportionality between the energy and the frequency of light. Einstein applied Planck’s theory and explained the photoelectric effect in terms of the quantum model using his famous equation for which he received the Nobel prize in 1921: E = h ν =ΚΕ max + W 0 (229 Where ΚΕ max is the maximum kinetic energy of the emitted photoelectrons and
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