mindmap root((PHOT)) photoelectric Involving an electrical effect produced by the action of light or other radiation.
🌱They wanted to avoid the kind of smoke detector that uses radioactive materials, so they've installed the photoelectric kind instead. 🌳The photoelectric effect occurs when light （or similar radiation such as X-rays） falls on a material such as a metal plate and causes it to emit electrons. The discovery of the photoelectric effect led to important new theories about matter （and to a Nobel Prize for Albert Einstein）. Photoelectric cells, or photocells, are used in burglar-alarm light detectors and garage-door openers （both employ a beam of light that is broken when something moves across it）, and also to play soundtracks on movie film （where a light beam shines through the soundtrack encoded on the film and is "read" by the photocells）. photovoltaic Involving the direct generation of electricity when sunlight or other radiant energy falls on the boundary between dissimilar substances （such as two different semiconductors）.
🌱Photovoltaic technology is being applied to thin film that can produce as much energy as solar cells while using far less semiconducting material. 🌳The -voltaic part of photovoltaic comes from the name of Alessandro Volta, inventor of the electric battery. Thus, unlike photoelectric cells, which use electricity for certain small tasks, photovoltaic （or PV） cells actually produce electricity. Solar cells, the standard type of photovoltaic cells （often called simply photocells）, operate without chemicals and with no moving parts to create energy directly from sunlight. Much research is now being done on creating an alternative technology—solar film, which could be stuck onto almost any surface, or possibly even sprayed on. photon A tiny particle or bundle of radiant energy.
🌱The idea that light consists of photons is difficult until you begin to think of a ray of light as being caused by a stream of tiny particles. 🌳It was Albert Einstein who first theorized that the energy in a light beam exists in small bits or particles, and scientists today know that light sometimes behaves like a wave （somewhat like sound or water） and sometimes like a stream of particles. The energies of photons range from high-energy gamma rays and X-rays down to low-energy infrared and radio waves, though all travel at the same speed. The amazing power of lasers is the result of a concentration of photons that have been made to travel together in order to hit their target at the same time. photosynthesis The process by which green plants use light to produce organic matter from carbon dioxide and water.
🌱Sagebrush survives in harsh climates because it's capable of carrying on photosynthesis at very low temperatures. 🌳The Greek roots of photosynthesis combine to produce the basic meaning "to put together with the help of light." Photosynthesis is what first produced oxygen in the atmosphere billions of years ago, and it's still what keeps it there. Sunlight splits the water molecules （made of hydrogen and oxygen） held in a plant's leaves and releases the oxygen in them into the air. The leftover hydrogen combines with carbon dioxide to produce carbohydrates, which the plant uses as food—as do any animals or humans who might eat the plant.