1. 13.1.1-13.1.4 Reading Recommendation: Pages 910-918

2.  A phenomenon in which a metal is struck by incoming light, which causes electrons from the metal to be emitted from the metal’s surface.  Examples where this can be observed:  Light shining on a negatively-charged electroscope causes it to be discharged  Light shining on a neutral electroscope causes it to become charged (positively)

3.  What is a photon?  It is a “packet” of light  “Quantized” light  Light acting as if it were a particle, not a wave, that is carrying its energy.  Wait…Quantized? What kind of word is that?  It means that there is a distinct, discrete amount of energy being carried by a “particle” of light, dependent on the qualities of the light.  Waves carry energy continuously, and in varying amounts/intensities depending on the position within the wave at which you look…continuous ≠ discrete

4.  Radiant light is emitted from objects that have a distinct amount of thermal energy (i.e. those objects that are at a measurable temperature emit radiant energy, the magnitude of which is dependent on the temperature)  If the kinetic energy of the atoms is discrete  And if the kinetic energy determines the temperature…  Shouldn’t the radiant energy being emitted also be discrete?

5.  IF the radiant energy being emitted from the hotter object is NOT discrete, then there is no way to show that energy is conserved during the thermal energy transfer from hot object to cooler object/surroundings  However, it has been shown time and again that energy IS conserved.  So Einstein is probably right.  (and earned the 1921 Nobel Prize in Physics as a result)

6.  Demo 1: https://www.youtube.com/watch?v=WO38qVDGgqw https://www.youtube.com/watch?v=WO38qVDGgqw  Demo 2: Phosphorescent strip (done in person in class )  Watch this video describing the photoelectric effect Watch this video  Demo 3 (watch at home): https://www.youtube.com/watch?v=kcSYV8bJox8 https://www.youtube.com/watch?v=kcSYV8bJox8

7.  Reminder:  An electronvolt (eV) is a measure of the amount of energy gained by an electron as it travels through a potential difference of exactly 1 V 1 eV = 1.6 x 10 -19 J  We will be using electronvolts as our energy unit throughout this topic!

8.  Objects with measurable temperatures will radiate heat in the form of radiant energy  Depending on the temperature, different wavelengths of light will be emitted

9.  Relates the wavelength of light with the temperature of the Black Body:  For example…determine the surface temperature of an object that predominantly emits in the visible spectrum:

10.  Relates the total energy being emitted by the blackbody to its temperature:

11. CCombining the Wien law and the Stefan- Boltzmann law, it was shown, classically, that WWhat happens as the wavelength gets shorter? Ultraviolet Catastrophe!

12.  Assumptions made to explain why the ultraviolet catastrophe doesn’t actually happen  Thermal Oscillators (the atoms emitting the radiation) have a specific, discrete amount of energy  Unlike blackbody radiation, the energy was not emitted in a broad, continuous spectrum  Energy was emitted in packets of energy, equivalent to the amount of energy contained by the atoms.

13.  Frequency of the emitted radiation is proportional to the energy the radiation carries away from the thermal oscillator.  Planck’s constant (an experimental value!) = 6.63 x 10 -34 J·s = 4.14 x 10 -15 eV·s

14.  The term given to the quantity hf  Planck’s hypothesis is used to explain quite a few phenomena not otherwise following a classical explanation.

16.  Calculate the energy of a photon of ultraviolet light, wavelength 3.00 x 10 -7 m. Express your answer in both Joules and in electronvolts.

18.  Watch this video after finishing your lab and after reviewing your notes:  https://www.youtube.com/watch?v=ubkNGwu_ 66s https://www.youtube.com/watch?v=ubkNGwu_ 66s

20.  The amount of potential needed to just stop the flow of electrons through the vacuum tube. The resulting current becomes 0 A  The stopping voltage is equivalent to the amount of kinetic energy of the emitted electrons