Page 47 - Alternative Energy Systems in Building Design

24 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

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LIGHT

A PHOTOELECTRIC Figure 3.1 The photoelectric
EFFECT EXPERIMENT effect experiment.

Einstein provided a theory for this that won him the Nobel Prize in Physics and laid the
groundwork for the theory of the photoelectric effect. Figure 3.1 shows the photoelectric
effect experiment. When light is shone on metal, electrons are released. These electrons
are attracted toward a positively charged plate, thereby giving rise to a photoelectric
current.
Einstein explained the observed phenomenon by a contemporary theory of quantized
energy levels, which was developed previously by Max Planck. The theory described
light as being made up of miniscule bundles of energy called photons. Photons impinging
on metals or semiconductors knock electrons off atoms.
In the 1930s, these theorems led to a new discipline in physics called quantum
mechanics, which consequently led to the discovery of transistors in the 1950s and to
the development of semiconductor electronics.

HISTORICAL AC/DC DEBATE BETWEEN EDISON AND TESLA

The application of direct current (dc) electric power is a century-old technology that took
a backseat to alternating current (ac) in the early 1900s when Edison and Tesla were hav-
ing a feud over their energy transmission and distribution inventions. The following are
some interesting historical notes that were communicated by two of the most brilliant
inventors in the history of electrical engineering:

Nicola Tesla: “Alternating Current will allow the transmission of electrical power to any point
on the planet, either through wires or through the air, as I have demonstrated.”
Thomas Edison: “Transmission of ac over long distances requires lethally high voltages, and
should be outlawed. To allow Tesla and Westinghouse to proceed with their proposals is to risk
untold deaths by electricide.”
Tesla: “How will the dc power a 1000 horsepower electric motor as well as a single light bulb?
With AC, the largest as well as the smallest load may be driven from the same line.”
Edison: “The most efficient and proper electrical supply for every type of device from the light
bulb to the phonograph is Direct Current at low voltage.”