Monday, January 29, 2007

Emitters and Reflectors

This is part 1 2 3 4 5 6 7 on the very Biblical subject of Light

What will happen when the crowd at the Superbowl gets excited? Hmmm? The answer is that they will let off a great roar. When the secondary leaps into space and snares the football out of the hands of the too-slow receiver the crowd will instantly excite and will not be able to hold it in. They will cheer. They will emanate sounds. They will emit shrieks of exhilaration. They won’t be able to help it because they will be quite stimulated and excited. By the way, this won’t happen very much, because Superbowls are generally boring and lopsided blowouts. If you want some real excitement, watch or play some Canadian football. Expansive fields that are 110 yards long and 65 yards wide, 12 men per team, two point conversions, 20 yard endzones, uprights on the goal lines, only 20 seconds between snaps, acres and acres of space between the hash lines, lots of legal motion, and only three downs. Try it and you’ll never go back. Superbowl? Piffle. Give me the Grey Cup any day. My attendance at the 1985 Grey Cup in MontrĂ©al cost me a rabbit dinner when the B.C. Lions beat my Hamilton Tiger Cats. It was a very good game though.

What will happen when the tungsten atoms in a lightbulb filament get excited? Hmmm? The answer is that they will let off a great light. When the switch is flipped and the electrons start to flow the tungsten atoms will instantly excite and will not be able to hold it in. They will heat. They will emanate bright light. They won’t be able to help it because they will be incredibly stimulated and excited.

The tungsten atoms absorb energy when the electricity is turned on. We won’t get into too many specifics, but the tungsten is a great resistor, and the act of forcing a flow of electrons through it excites the constituent atoms. They heat up, and in the twinkling of an eye they start to shine brightly.

If we were able to visualize an individual tungsten atom, we would see that its electrons get hyper when the power is turned on. We are familiar with the notion of electrons “in orbit” about the nucleus of an atom. What happens when electrons get hyper? You might expect them to just orbit faster and faster, but that’s not quite the way the quantum world works. What does happen is that an electron will get “promoted” to a larger orbit shell. This is the atom’s way of absorbing and storing energy. It shunts its electrons into higher energy zones.

These high energy electron orbit-shells are not usually stable. Sooner or later, the electron will have had enough and it will drop back down to its old shell. But as soon as that happens, the atom releases the energy it stored when it promoted the hyperactive electron to the outer shell. As the electron drops back down, this energy is released. In the terminology to which we have become accustomed, the energy is emitted in the form of a photon. The electron “emits” a photon as it de-energizes. Remember how photons are merely little packages of light? Well, light doesn’t sit still. That little packet of light vacates the premises vicinity at a high speed. At light-speed, actually.

That little photon joins gazillions of its companions to blaze forth from the lightbulb and light my way to the hallway to kick the cat for being obnoxious in the middle of the night.

That’s where light comes from. All light, every photon, comes from some sort of atomic level event, either an electron releasing its stored energy, or from other more exotic microparticle events. Light comes from energy release. Light is a form of energy.

My superb career in high school football was mostly spent in defensive pass coverage. My mission was to prevent the other team’s receivers from receiving the ball. It was my job to either knock that ball away from its intended recipient, or grab it myself. It was not my job to put up my arms and let it go right through them into the arms of the receiver, but unfortunately that sometimes happened.

Photons are tangible somethings. Photons have no mass, but they are pure energy, which is more or less the same as mass according to our friend Einstein.

Photons routinely run into things. They run into the glass of the bulb part of the light bulb, but for the most part they pass right through that, just like the ball passing through my useless flailing arms. They run into plaster walls, and they don’t generally pass through plaster.

If I turn on the light switch, and if my wall is green, then the light runs into a green wall, and I see a green wall. If no light runs into a green wall (i.e. it is dark), I don’t see a green wall. The green wall is not a source of light, but it is a reflector of light. Most of the photons crash into the green wall and get absorbed. The green wall eats photons. It eats red ones and ultraviolet ones and blue ones. They really don’t carry that much energy, so the wall is able to absorb them without too much trouble. Strange as it may seem, the green wall does not absorb green photons. It can’t do it. Instead, the green photons bounce of the wall, and find their way through my coke-bottle glasses and into my eye, and I see a green wall. I see a green wall because the wall doesn’t like green. Curious.

Anyways, all light that we see, every single bit of it has either been emitted straight from the original source on a trajectory straight into our eyes, or it has bounced off something first. The sun is an emitter. The moon is a reflector. My wife is a reflector. The fireflies that hang out in my parents’ yard in the summer are emitters. My car radio picks up emitted FM photons in the day, and at nighttime it can pick up AM photons from hundreds of miles away because they are reflecting off the upper atmosphere.

That’s it. Not very profound. All light has an origin. Light has to start somewhere. Everything, everyone, is either an emitter or reflector.

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