[Light Energy Explained]

light energy on Earth comes from the [Music] sun light energy from the Sun provides energy for the Earth and all living [Music] things but aside from the Sun anything that produces light on its own is a source of light a flame is a light source electric light [Music] bulbs even [Music] fireflies as different as these four sources are from one another they are alike in one way way an energy transfer takes [Music] place the light from a candle comes mainly from a glow of burning bits of [Music] carbon you can see this if the flame touches something like a cool dish chemical energy changes to heat energy and heat energy changes to light energy [Applause] in a light bulb an electric current causes a thin wire inside the bulb to heat up the wire becomes so hot that it glows electrical energy is changed to heat energy which is then changed to light energy certain insects and fish produce their own light changes in the glands of the Firefly cause chemical energy to be transformed into light energy here a firefly is glowing in response to a [Music] flashlight scientists believe that the sun's energy comes from nuclear reactions deep inside its core nuclear energy is changed to light energy [Music] why is heat energy often associated with light [Applause] energy what is this glow we see from light sources by studying how light behaves scientists have been able to develop theories about what takes place during energy transfers it's believed that what we see as a glow are photons streaming away from the light source to understand photons we have to start with atoms atoms are made of smaller particles every atom contains one or more protons in the nucleus with one or more electrons circling an orbit and many have neutrons the electrons carry a negative charge the protons a positive charge protons and electrons are attracted to each other somewhat like the poles of a magnet here's a hydrogen atom with one electron circling the nucleus in a small orbit when heat or electrical energy is added to the atom the electron jumps to a larger orbit but the attraction between the proton and electron makes the electron jump back to a small orbit the energy that makes the electron jump to the larger orbit is released when the electron jumps back energy called a photon as long as there's an input of energy there's an output of energy this can be light or other kinds of [Laughter] energy and that's what we see as a glow from the Sun from a candle a light bulb or a [Music] firefly photons streak away from a light source at 300,000 kilm a second that's fast enough to go around the world seven and a half times in a single [Music] second photons move in waves with crests and troughs the length of one cycle is a [Music] wavelength what we see is white light is really a jumble of phot tons of different wavelengths mixed together when a prism splits white light into a rainbow of colors each color represents a different wavelength red at one end of the spectrum has a longer wavelength then Violet at the other [Music] end what we see as a band of colors is called the spectrum of visible light we say visible because what we see as light is only a part of what is actually there there is also invisible light the photons with longer wavelengths just beyond the color red are called infrared which we sense as heat only without light the visible light spectrum is only a small part of a much wider Spectrum longer wavelengths include microwaves radar TV and radio waves then there are photons with shorter wavelengths Beyond Violet called ultraviolet it's the photons of ultraviolet that cause Sun Tans and sunburns Beyond ultraviolet the wavelengths become shorter x-rays gamma rays cosmic rays the wavelengths are so short that the photons act as Tiny packets of energy that can penetrate matter for instance when you take an x-ray photo all together these photons of visible and invisible light are called the electromagnetic spectrum the word Photon comes from two Greek words photo which means light and on which means particle Photon light particle yet from what has been observed by scientists a photon is not a particle but a particle wave it is a particle that travels like a wave we can see the w wavelike nature of photons every time we use a pair of polarized sunglasses I'm going to get this polarized glasses have lenses containing tiny crystals in parallel rows the light traveling on the same plane as the parallel crystals can pass through Rays traveling on other planes are reflected a photoelectric cell transforming light energy into electrical energy demonstrates how photons act like particles a photoelectric cell is usually two Thin layers made mostly of silicon when the particle like Photon strike electrons in the photoelectric cell electrons are released causing an electric current to flow on this demonstration house trailer with photoelectric cells on the roof the cells provide enough electricity to run all the appliances inside the time may come when much of our electrical energy is produced by photoelectric cells some of our light energy needs might even be met by chemical means like those taking place inside a [Music] [Applause] firefly the idea of using the Sun's light as an energy source is as old as mankind although drying clothes with scattered photons from the sun takes quite a while but when photons are concentrated with a magnifying glass they pack a lot of [Music] energy on a huge scale curved mirrors can focus sunlight on a tower here water is heated to make Steam and the steam generates electrical energy perhaps the most important light energy transfer takes place between the Sun and green plants [Music] photosynthesis [Music] this energy transfer has been going on for hundreds of millions of [Music] [Music] years the fuels we use to make our electrical and heat energy coal petroleum and natural gas were once ancient plants which remain today as fossils containing stored energy from the Sun there are other light sources besides the Sun but it's the energy in sunlight that makes life possible on Earth so just in case you thought light energy was only to see by remember that without light energy there would be no plants no animals no you or [Music] me oh