Film loop: Photoelectric effect, 4:02 min.

Film Loop: The Photoelectric Effect Length(min.):4:02 Color: No Sound: No. Electromagnetic radiation consists of energy packets called photons. On impact with a material particle, a photon ceases to exist and all of its kinetic energy is transferred to the struck particle, e.g. an electron. If such an electron is in a metal near the surface, this added energy may be sufficient to permit the electron to penetrate the potential energy barrier at the surface and escape from the metal. Electrons which have been ejected in this way are called photoelectrons and the phenomenon is known as the photoelectric effect. In the film, a zinc disc is connected to an electroscope. The electroscope is charged and a mercury vapor lamp pointed at the disc. The first two times, the electroscope is discharged; the third time, it stays charged. Q288.1 What was different about the third attempt? (Hint: Watch Film-Loop 80-284.) Q288.2 If we agree to call the charge on the plastic rod 'negative', what is the sign of the excess charge on the zinc disc in each of the three demonstrations? Q288.3 If the electromagnetic radiation liberates only electrons from the metal, in which case(s) must there have been more electrons near the surface? Q288.4 If we assume that the electrons themselves are charged, what sign must we assign them under the convention we have been using? Q288.5 Discuss the differences between the photoelectric effect and the point discharge shown in Film-Loop 80-284. When an ordinary incandescent bulb is substituted for the mercury vapor lamp, the electroscope stays charged - even though the bulb appears quite bright and is held quite close to the disc. When the lens of the mercury vapor lamp is covered with a piece of window glass, the blue light that comes through also fails to discharge the electroscope, but when a piece of quartz is used, the photoelectric effect occurs again. Q288.6 What kind of radiation can get through quartz but not through glass and, thus, appears to be the active component in the output of the mercury vapor lamp? Q288.7 If the intensity of light doesn't seem to have anything to do with producing the effect, what is the property of the radiation that counts? Q288.8 How would this account for the differing results from visible light and the mercury radiation? Q288.9 The cardboard seems to block the photoelectric effect even when the mercury vapor lamp is used. Would a cardboard shield protect a charged electroscope against all types of radiation? Q288.10 When the zinc is turned around, you can see that the other surface is relatively dull. Now, the mercury vapor lamp fails to produce the effect. When this same surface is cleaned with abrasive, it works as well as the first side did. Why isn't the effect produced with the dull side? Q288.11 Do you think visible light might work if the disc were made of something other than zinc?