Cerenkov Radiation
Spark
Coriolis Effect
Parity
Cerenkov Radiation
Cerenkov radiation happens when a particle travels faster than the speed of light. That the particle is traveling faster than "the speed limit of the universe" can mislead one to think that the laws of Relativity are being broken. However, since Cerenkov radiation always happens in a medium, such as water, light is slowed down proportional to the index of refraction of the medium. Therefore, the particle can be moving faster than the speed of light through the medium. This creates a shockwave of electromagnetic radiation. It's comparable to the sonic boom produced when a plane travels faster than the speed of sound.
Cerenkov radiation is observed in nuclear reactors. During fission, a beta particle is created and travels outward faster than the speed of light. This makes the water in the reactor glow in ultraviolet and blue visible light.
Cosmic rays interact with the atmosphere and create various particles, including neutrinos and muons. When these particles move through the very pure water in a detector tank - in Kamiokande for example - they move faster than the speed of light. A cone-shaped shockwave is created and detected by the photomultiplier tubes.
February 9, 2004 Top
Coriolis Effect
The centrifugal force is equal and opposite in magnitude to the centripetal force but isn't really a force. The centripetal force points inward relative to the circular path and is tangential to the velocity of the object. If the centrifugal force were real, it would cancel out the centripetal force, the body would be in equilibrium and it would travel in a straight line. However, if the system is analyzed in a rotating reference frame, the forces can cancel out and the object still has a rotating inertia and moves in a circle.
The Coriolis force is due to a rotating reference frame. When the motion of a body on the earth is described, the earth is usually taken to be an inertial reference frame. Of course, the earth is rotating and revolving around the sun, and our solar system is part of a moving galaxy which is part of a moving cluster…and things get complicated since the coordinates on which the calculations are done are constantly changing. The apparent deviation in the motion of an object in a rotating reference frame is called the Coriolis force. The magnitude of the effect is proportional to the momentum of the object and the angular velocity of the reference frame. The force acts perpendicular to the velocity of the object.
The most prominent effect of the Coriolis force is in storm patterns since they are very massive and fast. In the northern hemisphere winds are deflected to the right and in the southern hemisphere winds deflect to the left. Therefore, low pressure systems, such as tornadoes and hurricanes, rotate clockwise. Sunspots also exhibit clockwise or counterclockwise motion influenced by the Coriolis force. Airplanes also have to take the effect into account when flights are planned.
Another seemingly non-existent force is the Casimir force, where two mirrors separated by a vacuum are attracted to each other. The vacuum is commonly defined as empty space, but thanks to quantum mechanics there are always field fluctuations and particles blinking in and out of existence everywhere. The vacuum fluctuations are reflected back and forth, amplify and the plates are forced together. The Casimir force has been proven experimentally, and it supports that there are eleven or more dimensions.
February 18, 2004 Top
Spark
A spark is also called a dielectric breakdown. Lightening is a familiar example of dielectric breakdown and happens about a hundred times each second all over the world. During a storm, negative charge builds up on the bottom of the cloud. The intense electric field created between the earth and the clouds (or between two clouds) partially ionizes the air and it becomes a conductor. The charge on the cloud can now travel through the air to the earth, and this current is the lightening. Heat is generated by the current and the air "explodes" and a blue-white flash is seen.
Sulfur hexafluoride acts as a dielectric and an insulator in the VanDeGraaff's big red tank. The maximum amount of electric field a material can withstand before it changes from an insulator to a conductor is called its dielectric strength. The sulfur hexafluoride has a very high dielectric strength and therefore prevents dangerous sparks from forming. Other dielectrics used in high-voltage engineering are carbon dioxide and nitrogen.
February 26, 2004 Top
Parity Violation
Mathematician Emmy Noether proved in second decade of the twentieth century that a conservation law implies a symmetry and vice versa. Tsung-Dao Lee and Chen-Ning Yang received the Nobel Prize in 1956 for their work on CP (charge conjugation and parity) violation, therefore proving that the universe is not symmetric.
The CPT Theorem states that all things are symmetric when charge, parity and time are inverted simultaneously. For example, another universe composed primarily of antimatter, whose time flowed backwards relative to our own, and was mirrored would have the same physical laws as our own.
Chein-Shiung Wu carried out the experiment proposed by Lee and Yang to test for symmetry. She aligned the spin of radioactive Cobalt 60 with a magnetic field. Beta particles were emitted primarily in the same direction as the field. After parity inversion of both spin direction and magnetic field, more beta particles were emitted in the same direction as before (this time opposite the magnetic field). Absolute parity conservation would require the most particles to always be emitted with the direction of the magnetic field. This proved that parity was violated when the weak force (responsible for nuclear decay) was involved. Another proof of parity violation is that a left-handed neutrino under a P transformation (a right-handed neutrino) has never been found.
The experiment verifying charge violation was done in a similar fashion, using muons instead of Cobalt. The muons decayed into muon neutrinos and electrons, and the direction of emission of electrons was observed mainly in one direction. A C transformation required the use of an antimuon, and its antielectrons were emitted in the same direction as the muon's electrons. Thus, the violations of charge and parity symmetry in the weak force were verified.
The carriers of the weak force are the W and Z bosons. W interacts only with left-handed particles and is involved in nuclear decay. Z interacts with both, though mostly left-handed. Therefore, only left-handed quarks interact weakly.
The lack of CP symmetry in the very early universe influenced the fact that there is so much more matter than antimatter today. However, CP violation only accounts for a very small discrepancy. Many believe that there is something more to the standard model that would explain this.
April 12, 2004 Top
© 2004 Azure Hansen
