Alabama Public Television Video: Einstein Videos http://www.aptv.org/VideoRoom/nola.asp?NOLA1=EIN Video episodes of Einstein Videos from Alabama Public Television. Color Mixing http://www.aptv.org/VideoRoom/viewprogram.asp?FileID=704 What is light? How does it travel, and how fast can it go? Even as a teenager, Einstein was fascinated by the nature of light. When he was just 16 years old, Einstein tried to imagine what it would be like to ride on a beam of light. Could he travel as fast as light? Could he travel faster? Color Mixing http://www.creativecommons.org/licenses/by-nc/1.0 nonadult Alabama Public Television Speed of Light http://www.aptv.org/VideoRoom/viewprogram.asp?FileID=703 Einstein's crucial breakthrough about the nature of light, made in 1905, can be summed up in a deceptively simple statement: The speed of light is constant. So what does this sentence really mean? Surprisingly, the answer has nothing to do with the actual speed of light, which is 186,000 miles per second through the "vacuum" of empty space. Instead, Einstein had an unexpected insight: that light from a moving source has the same velocity as light from a stationary source. For example, beams of light from a lighthouse, from a speeding car's headlights and from the lights on a supersonic jet all travel at a constant rate as measured by all observers—despite differences in how fast the sources of these beams move. Speed of Light http://www.creativecommons.org/licenses/by-nc/1.0 nonadult Alabama Public Television General Relativity http://www.aptv.org/VideoRoom/viewprogram.asp?FileID=702 Space-Time is the unification of space, the three dimensional world around us, and the concept of time. These seemingly immiscible ideas must meet to explain the nature of light. Space and time are not absolutes: 10 seconds is not always 10 seconds and a cubic centimeter is not always a cubic centimeter. The speed of light in a vacuum is the only absolute. General Relativity http://www.creativecommons.org/licenses/by-nc/1.0 nonadult Alabama Public Television Photo-Electric Effect in Action http://www.aptv.org/VideoRoom/viewprogram.asp?FileID=701 The understanding that light interacts with matter like a particle also lead to modern information technology, like computers, TVs, and lasers. The communicator is a direct example of the Photo-Electric Effect, one of Einstein’s groundbreaking 1905 theses. This is the achievement for which he won the Noble Prize for Physics in 1921. The Photo-Electric Effect centers on the ability of light to free up electrons inside metal atoms. This induces electric current through out an illuminated piece of metal. The idea that light can physically disturb electrons denotes a particle nature of light. The energy produced is proportional to the frequency of light, not the intensity of light. This fact draws on the wave-like properties of light within the same interaction. Photo-Electric Effect in Action http://www.creativecommons.org/licenses/by-nc/1.0 nonadult Alabama Public Television Photo-Electric Effect http://www.aptv.org/VideoRoom/viewprogram.asp?FileID=700 The message is the dual nature of light. When a gaseous element is raised to a high temperature, the atoms emit radiation having discreet wavelengths. The set of wavelengths for a given element is called its atomic spectrum. Einstein showed us that light can be described not only as a wave, like a water wave, but also as a particle. This understanding of light allowed us to understand why different elements have different fingerprint patterns of light known as spectra. Photo-Electric Effect http://www.creativecommons.org/licenses/by-nc/1.0 nonadult Alabama Public Television Light Diffraction http://www.aptv.org/VideoRoom/viewprogram.asp?FileID=699 This demonstration exhibits light’s wave-like characteristics. This is half of light’s duality; the other half being light’s particle-like characteristics. Using diffraction gratings we can compare the visible parts of atomic spectra for different elements. A diffraction grating consists of a large number of equally spaced parallel slits. These slits bend light differently according to wavelength. Incandescent lights work by heating a solid piece of tungsten wire. This heating of a solid produces a variety of wavelengths, giving an impressive spread of colors when viewed with a diffraction grating. Since the other lamps are single gaseous elements, they emit only a few wavelengths of light, their individual atomic spectra. Light Diffraction http://www.creativecommons.org/licenses/by-nc/1.0 nonadult Alabama Public Television