Journey into the Atom: Advanced Topics in Particle Physics

[an error occurred while processing this directive] Journey into the Atom: Advanced Topics in Particle Physics

The following sections are in-depth interactive examples of advanced topics in particle physics. They are completely independent of each other, so feel free to browse through the ones you want. Don't feel ashamed if you are confused by this information; even majors in this field have trouble understanding some of this stuff! You may want to review scientific notation in the debriefing.

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The electromagnetic spectrum is the series of all frequencies that electromagnetic radiation can have. It ranges from radio waves to visible light to X-rays and beyond. Here is a chart showing where various types of radiation are on the spectrum:

The wavelength of electromagnetic radiation is the distance between any two corresponding points on a wave. The frequency of the wave is how many times it repeats itself a second, a unit known as Hertz and abbreviated 'Hz'. Most of us have actually used this before when describing computer chips. "...with an Intel Pentium II Processor running at 233 MHz...". The 233 MHz means it does 233 Million cycles every second.

The wavelength and frequency of electromagnetic radiation are inversely related; their product is a constant, the speed of light (3.0×10⁸ meters/second). Here you can calculate one of the values from the other:

The photon is said to be the particle of light. Now, most of us don't think of waves of electromagnetic radiation (like radio waves and microwaves) to be made of tangible things. The reason scientists think of light this way is because energy is "quantized", or, more simply, it comes in units. The photon is said to be the smallest amount of energy you can have in a particular wave. The cumulative energy also has to come in multiples of this quantized amount. A good analogy to this situation is water, which seems to be a flowing substance, but is actually composed of tiny molecules. Also, there can't be half a molecule, so there has to be some multiple of molecules and atoms in the liquid. The energy of a "quantum", or packet, of light energy can be calculated by multiplying its frequency by a number known as Planck's constant (6.626×10^-34 Joule-seconds). Here you can input either the frequency or wavelength of the light and find out how much energy a single photon of that light contains:

The observation that light waves seem to behave like particles (see above) prompted some scientists to wonder whether particles behave like waves. At high speeds, particles unmistakably behave as if they were waves, and that is the basis for the electron microscope. Louis De Broglie experimented a little and found that the faster the particle meaning any mass) travels, and the less massive it is, the smaller the wavelength. You may want to read that over a couple of times until it makes sense. Here you can calculate the De Broglie wavelength of a particle according to an equation derived by Louis De Broglie:

Here are some common values [for the equation, that is]:

Object Mass Speed

Electron 9.11e-31 kg

Baseball being pitched 0.5 kg 40 km/h

Car on a highway 1000 kg 35 km/h

Object	Mass	Speed
Electron	9.11e-31 kg
Baseball being pitched	0.5 kg	40 km/h
Car on a highway	1000 kg	35 km/h

The Heisenberg Uncertainty Principle states that the position and velocity of a particle can never be known exactly at the same time. It seems weird, but it is true. For each thing, no matter what it is, there is some amount of uncertainty of its exact position and velocity. Remember, velocity is speed and direction. The product of the uncertainties in velocity and position must be greater than a constant divided by the particle's mass (say that over again a few times). The reasoning behind this is that at the sub-atomic level, the act of measuring either the position or velocity of a particle changes the value of the other property. To make the measurements, you will have to fire a number of other particles and try hit the particle. The more massive the particle, the less it is disturbed by these measurements. Of course, we can't explain it all in a nutshell, but reading books on the Individual Exploration page will definitely be able to give a more in-depth explanation. The equation is exactly the same as the De Broglie equation except that the wavelength is replaced by the uncertainty of position and the speed is replaced by the uncertainty in velocity. Also, remember that these uncertainties are actually minimum uncertainties; just because you get a certain value from the equation doesn't mean that you can't make a more inaccurate measurement.

Some of the most important principles in physics are the conservation laws. The conservation of mass was one of the first of these rules to be discovered. Another long-known law was the conservation of energy. However, when Einstein discovered that mass could become energy and vice versa, the law of conservation of mass-energy replaced the other two rules. This is an excellent example of a law which does not apply in specific circumstances. The two original laws were not wrong, they were just incomplete. The same situation applies to various parts of science. Most of the greatest discoveries in science were not finding an entirely new phenomenon, they were usually merging two fields which were previously thought to be completely unrelated. If physicists can create a "Grand Unified Theory" (GUT), it will be quite an achievement, since it will describe the electromagnetic, weak, and strong forces as different aspects of the same force. The theory which combines gravity with those three will be called the "Theory of Everything" (TOE). Anyway, back to conservation laws. Many of these apply only to specific situations, that is, they are only conserved in particular interactions. For example color charge is not conserved in the weak interaction. However, it seems that momentum, angular momentum/spin, mass-energy, and electric charge are conserved in all four interactions. Here is an example of how to use the conservation of electric charge in an interaction: