Discover How To Expand Your Knowledge of Physics and Get a Clear Understanding of All Physics Levels-With an Expert to Answer Your Questions You Can Never Go Wrong…
Articles
What Is All that Talk about Spectral Lines?
by Thomas Oestereich
Have you ever seen a rainbow? Can be pretty spectacular. Where do all the colors come from, with the sunlight being more or less white?
A rainbow can be seen when the air is full of millions of minute spheres, water droplets which reflect the sun rays from their inner surfaces. The white light from the sun happens to be a mixture of a wide range of colors, and the small droplets reflect different colors into slightly different angles, thus separating them.
The same principle can be seen at work with a suitably formed piece of glass, a prism. Let white light shine through a slit and then a prism, and the different colors which build up the white light are refracted to slightly different directions, so when they fall on a screen, different colors can be seen at different places. This analytical picture of light is called a spectrum.
In both cases the itinerary of the light from air through a more dense medium plays a role. If you don't limit the dimensions of your light source, then on the screen, all the different colors fall on top of each other leaving you with white again. That's why we take a slit in front of the prism and are able to see its colored pictures at different places on the screen.
Now the sun is a very big very hot mass. And big hot masses tend to send out continuous spectra. This has to do with the way how the light of these hot masses is created, namely by collisions of fast moving free particles which have all kind of speeds, all kind of energies, and in the collisions get rid of that energy in the form of all kinds of light.
But if you produce light by other processes than collisions of hot free particles, you get different results. If electrons in atoms are excited, meaning: pumped up with energy, they have only discrete "places" they can occupy. They can only take up and give back energy in discrete chunks.
What has energy to do with color of light?
Although light is a wave, an electromagnetic wave, this wave can only take up and give out the energy it holds in parcels. The size of a parcel is connected to the color of that particular light wave. Blue light exchanges bigger parcels of energy than red light. That's why the discrete chunks of energy emitted by electrons in atoms as light, result in light of characteristic color, every color for one of the possible differences in energy of the positions these electrons can occupy or leave.
So they send out light of colors which correspond to the energy differences between those "places" they occupy. These chunks of energy are pretty narrowly determined, so the corresponding color is equally narrowly defined. What you then get on the screen past a prism, is a bunch of lines with different colors.
Now every substance has a bunch of lines or a spectrum which is specific for just that substance. That is why the yellow helium line, first found in the sun's corona during an eclipse 1868, was significant: There was no known element with that line. And only elements could exist so near to the sun, no compounds.
Today the spectral analysis is a standard procedure. At those days it was still new, and the fact that a new element was found in the sun before it was found on earth was kind of a sensation.
Keep your heart open to be surprised by the wonders of nature and the evolution of human insight into its principles.
For an ordinary view on select chapters of physics, have a look here: http://physics.global-momentum.net/
Regards Thomas Oestereich
After 20 years of being a physicist, Dr. Thomas Oestereich turned from scientific research to a life as an author and editor of his home school curriculum. He now seeks to help his readers gain access to the insights of physics. Bringing the achievements of science to a larger public, he hopes to finally contribute to a better knowledge of the options and constraints of decision making in our democratic society.
http://www.physics.global-momentum.net
Contact the author, Thomas Oestereich
, at speed-up@gmx.net
.