Radiation From Within

Hello reader,

Can you classify the Sun and a steel ball in the same category? What do you think? I think so. I know the Sun isn't metalic, but it is shiny... right? Right? Historically, this is the mother of Quantum Physics. The very beginning. Plank did well.

Anyways, the Sun and the steel ball can be categorized as... A Black Body! Do think of it the wrong way, think of black body as a scientific object. Let's dissect the word first, then we can check other fun properties.

Black: it's a shade in our "colour" scale that as my grade 8 art and grade 9 science teachers put it, "Absorb all light". White is different. It reflects all light. So if a perfectly black object absorbs all light, it is unable to reflect any light. Using this defintion of black, we can then define Black Body as an object that absorbs all light directed at it without emitting any light back (reflecting light).

The Sun can be considered a black body (Before I go any further, there is no such thing as a perfect black body in our known universe. There is only what we can approximate to be black bodies.). But you ask, why are we able to see white light emitted? This is what puzzled physicist Maxwell Plank. Not only that but with old models, we would have the Ultraviolet Catastrophe. So what changed?

Maxwell looked at the Sun (not for very long though) and thought that maybe what is being seen, was thermal energy. Energy, in the form of heat, was being converted to electromagnetic energy (light). So he figured out that the old models were wrong, and that his new formula and idea of light packets (or quanta) would help explain the empirical (experimental) data (as shown in the picture).

This new model indicated that at certain temperatures, there was a maximum intensity for a given wavelength. As the temperature increases, the maximum intensity of the wavelength increases. If you take the integration of this curve, you get infinity. The area under the curve is the energy per unit volume.

This was the problem with the old model. When you integrated the curve from 0 to infinity (wavelengths) it would say that you get infinite energy! Most of this energy was in the ultraviolet spectra. This was cause for concern! How could something forever be emitting UV radiation. This did not get picked up by health critics because they did not know of the adverse affects of UV radiation at the time.

So in all, a black body is something that emits thermal energy in the form of light and light like radiation. Oh and by the way... The steel ball, it is considered a black body at about 1000 K or 1273 degrees Celsius.

Bored of Bohr?

Hey Reader,

What is that weird word ion the title: Bohr? Well, here we are talking about the physicist, Neils Bohr, the man responsible for the High School model of the atom! You know, that model that mimics the solar system. How did it come about? Why is it useful? Why is it used?

To start, lets see the history of the atom and the models. It started with Dalton, when he stated that the atom is the smallest unit of matter. He also stated that the atom is just a solid ball (such as a billiard ball). This formed the first theory of the atom

.

Then came J.J. Thompson, who realized that a charge can be induced onto the atom. Negative or positive, there has to be a way to charge an atom. He devised a model (sometimes called the plum-pudding model) in which allows the charges of the atom to be spread-out in a "solid" atom.

50 years later, a famous experiment, called the Gold Foil experiment was performed by Ernest Rutherford. His discover shocked the world of science. He shot positive particles (alpha particles) through a thin gold foil and placed detectors at different angles. He observed that many alpha particles was deflected at very small angles. they almost

passed right through!. How could this be unless there was a central nucleus with a positive charge. Thus, we learned that there was a central positive nucleus.

Borh showed that electrons are in orbits. Shown above, electrons circle the nucleus like planets around the sun. The first orbit holds 2 electrons, the 2nd and 3rd each have 8. This is NOT what the current model represents, but this is widely used in many people's education.

This model is useful because it explains a weird phenomenon

. Certain elements emit a certain spectra of light. To the right is a small spectrum (known as the Balmer) that is emitted from Hydrogen. Hydrogen emit other visible lights as well. How can this be explained unless electrons can get excited to different orbitals and de-excited states to lower orbitals. To produce light, with this model, an electron must go from a higher orbital to a lower orbital (Blamer series goes from any higher orbital to the 2nd orbital). This can be mathematically explained using the Rydberg-Balmer equation. The wavelength is correlated to the difference of squared orbitals.

Even though a more accurate model has been discovered, called Valence Shell Electron Pair Repulsion (VSEPR) theory, Borh's model is a very basic model that works well with the spectral phenomenon. We use it so we can better understand the light.