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This text is meant to accompany class discussions. It is not everything there is to know about uniform circular motion. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)
Click for the questions that go with this reading
Electric Field Applications

 

Radios, cellphones, garage door openers, many televisions and radio controlled toys use electric fields to communicate.

The electric fields do not exist inside of a sealed container that is made of a conducting material. The do exist inside of a sealed container that is made from an insulating material. A sealed container made from a conducting material is called a "Faraday Cage." Faraday cages block electric fields from entering the"cage." Much more detail is covered in the class notes -online.

Fish, some amphibians, and three mammals possess a sixth sense called electroreception. Electroreception allows an animal to perceive electric fields. Electroreceptors allow these animals to sense the electric fields in other animals. To sense the electric fields of others, these animals need to be in a conductive environment. This means a very wet environment. Some fish have active sensors that generate their own electricity instead of only sensing others.

Anything with separated charges is a battery.

The positively charged hand is the positive pole of a battery while the negatively charged doorknob is the negative pole of a battery.

The combination of a thunderstorm cloud and the Earth create a battery.

They generate huge electric fields between the clouds and the ground and between the bottom of the cloud and the top of the cloud. These fields are responsible for lightning.

Separated charges generate an e-field between these two points of separation. This electric field provides the force to move energized charges in a circuit. As an analogy think of the the movement of charges in a wire like water in a river. The electric field provides the push that generates a current. The water is not used up as it flows over a water fall. Instead, its potential energy extracted from the water as it is used to turn turbines at the bottom of the water fall to generate electricity. In the same way, charges flow through a wire and some of their energy is used up to power electronic devices.

 

Ionic Wind

 

The electric field concentrates on corners and sharp points. The pencil shown below shows how the electric field bunches at the point.

Where the fields concentrate so does the force. When the electric field's force is large enough, the molecules in the air get broken apart. When gas molecules get broken apart into smaller charged pieces, it is called ionization. Like charges are ejected and the gas ionized where the force is the greatest, at the sharp point. These charges coming off the pencil have the same charge as the object. (The term "sharp point" is relative to the size of the object.) If the pencil below has a net negative charge, then the ionic wind coming off the pencil also has a negative charge.


Lightning Safety
  • You are safe in a metal car because of the Faraday cage you are sitting in. It has NOTHING to do with the rubber tires -PERIOD!
  • In a lighting storm do not attach yourself to the outside by a cord or path such as a corded phone, corded keyboard, corded game controller. Wireless equipment is safe to use.
  • Don’t wash your hands, if possible, with running water.
  • Don’t take a bath or shower. Lightning can travel through the water and into you.
  • Close all windows and doors. Bolts of lightning can travel on the wind blown in.
  • If you are in field, too far from a building when your hair stands up and your skin feels prickly, squat on the balls of your feet. Do NOT put you hands on your legs, knees or the ground while squatting. NEVER lay down.

 

Millikan's Experiment

 

In 1909 Robert Millikan conducted an experiment to whose purpose it was to calculate the charge on an electron. They flooded a vacuum chamber with small charged oil drops. These drops where pulled down by gravity. Millikan applied an electric field inside the container. Many of the charged oil drops became suspended. He used this information to calculate the electron's charge. This experiment showed that charges occurred in integer multiples of 1.60 x 10-19C. This is absolute value of an electron's charge, or a proton's charge. This charge is called the "elementary charge." For over half a century, the elementary charge was believed to the smallest possible charge. (Until physicists got new data.)

Above is a one minute video explaining Millikan's experiment. It is from YouTube. Here is its actual address, http://www.youtube.com/watch?v=XMfYHag7Liw, by HerrPingui , uploaded April 22, 2008 accessed April 5, 2010.

The "elementary" charge was taught as the smallest possible charge. It was discovered from Millikan's experiment. However, we now know that it is not the smallest charge. The smallest charge is considered to be 1/3 of the elementary charge. It resides in something called a, "quark."

Quarks ... The very, very, very short summary

Below is what an introductory chemistry teaches as the appearance of an Helium atom.

In 1964 Murray Gell-Mann and George Zweig mathematically predicted the exist of fundamental particles called quarks. These quarks possess 0, +1/3, or +2/3 of an elementary charge. Quarks combine to make up many subatomic particles. Because of what we know of quarks, there's more to a helium atom than what chemistry taught.

Quarks changed what Millikan conclusions. Millikan got the charge of an electron correct, but an electron or proton's charge is not the smallest possible charge. Below is some of the currently known information about quarks:

Quark Symbol Charge Mass*
Up U +2/3 1.7 - 3.3 MeV
Top T +2/3 172 GeV
Charm C +2/3 1270 MeV
Down D -1/3 4.1 - 5.8 MeV
Strange S -1/3 101 MeV

Bottom

 

B -1/3

4.19 GeV or
4.67 GeV

*These masses are estimates because quarks have not lasted or been found by themselves..

 

 

Physicists often refer to these six quarks as "flavors." (A chemistry class analogy to the term flavor might be the term isotope. For example, an atom with 12 protons is called "carbon." But the carbon molecule has several types with 8 to 22 neutrons, e.g. carbon-12, carbon-13, carbon-14, etc.. These types with different neutrons are called isotopes of carbon.) Similarly, there are 6 flavors of a quark. Without going into too much detail, it takes three quarks to create any of the particles of the nucleus. Protons and neutrons are created with quarks. Electrons are NOT created with quarks. Quarks are a fundamental part of "The Standard Model." The twelve smallest particles that are combined to make a particle with mass are called a "Fermions." (They are the particles in the pink and blue rectangles in the table below.) Fermions are further separated into "Quarks" and "Leptons." The standard model is use to explain the existence of other particles, forces and how they interact with the environment. Below is a table depicting the standard model as of July 2012.

Standard Model

(Click here for a larger image of the graphic shown above.)

These particles combine to make other particles. The fermions above are called "elementary particles" because they cannot be made by adding other particles together. The electron, muon, and tau are the charged leptons. These leptons combine with other particles and are easily observed. The neutrinos make up the other three leptons. The neutrino comes in 3 flavors; electron neutrino, muon neutrino, tau neutrino. These three neutrino's do not interact with other particles well and are therefore hard to find.

The masses are an educated guess. Quarks are found in larger particles like protons and neutrons. When scientists try to knock a quark out of a proton, the quark gets to a point where it could be seen. But it's energy is too high and an anti-quark is produced. As a consequence, the quark its antiquark are annihilated and neither is observed.

In toto, the standard model can be considered rather unwieldy. Upon closer inspection it contains a total 36 quarks and anti-quarks, 19 or more free parameters, and 3 generations of redundancy. This theory only accounts for about 4% of the mass/energy content in the universe. It does not account for dark matter (estimated to be 23% of the universes mass,) or dark energy, (estimated to be 73% of the mass in universe.) Perhaps string theory or some variation of string theory may explain everything. OR, we need a new theory yet to be discovered.

The idea behind "String Theory" or "Super String Theory," is that insides of quarks contain little filaments of energy. Each vibrating filament vibrates at a different frequencies. These frequencies determine the properties of the particles. The frequencies determine if the particle is an up quark, a down quark, or an electron. Super String theory describes 10 dimensions of space and one of time. "Super String Theory," is not accepted by all physicists. "Strings" are so small that nobody can measure them. Basically, our measurement tools are too big. So proving string theory will be difficult. Perhaps the search for "dark matter" at the Large Hadron Collider will shed some light on strings.

The Strong Force
How is it that two or more protons can exist together so close to each other inside the nucleus. Because they are like sign charges, they are repelled from each other by a force of electrostatic repulsion. They follow our rule that like charges repel each other. (This repulsion force is due to Coulomb's Law. Sometimes it is refereed to as the "Coulomb force." This is brought up in a later chapter.) The question remains, how do two like charges stay so close to each other. As it turns out there two forces acting on the protons and neutrons while in the nucleus. The strong force also acts within the nucleus. But only other forces, it gets weaker as the distance between particles increases. Some describe make the analogy that is is like balloon. once you stretch to certain limit, the balloon pops and the force disappears.

Hadrons
Particles made form a combination of quarks and anti quarks are Hadrons AND interact with the strong force. The proton is the only hadron particle that is stable. Being stable means that is will not decay into a different particle and disappear. The neutron is only stable when it is inside of the nucleus. If the neutron is removed from the nucleus. It decays and disappears. All other hadrons are unstable and decay away.

Large Hadron Collider
In order to see what is inside the particles that are in a molecule, we need to break them apart by slamming them together. When they slam together they break into pieces and physicists look at the pieces to see what's inside the particles. Because there particles have a charge they can be pushed around with electricity and magnetism in what is called a particle accelerator. (Later in the chapter, plans for making a hand held particle accelerator for shooting electrons will be analyzed.) Most particle accelerators use electrons since they are 1000 times lighter than a proton. To see inside of a proton means you have to build something powerful enough to move the heavy protons. To do this scientists and engineers as CERN designed and built the LHC along the border between Switzerland and France. LHC stands for large hadron collider and CERN stands for European Council for Nuclear Research. In this case the word nuclear means very small particles -not bombs. Since teh LHC only accelerates stable hadrons, it would be more meaningful to the general public if they called the facility the LPC, Large PROTON Collider. Oh well, those crafty physicists are trying to teach us something with their name choice.

This is a map showing the overlay of the Large Hadron Collider. Source: http://faculty.fullerton.edu/cmcconnell/304/Images/LHC.JPG
Go here if you want to see more images from the Large Hadron Collider.

Baryons and Mesons
If a particle is made of quarks , then it is a hadron. If it is made from an odd number of quarks it is a Baryon. If it is made from an even number of quarks, it is a meson. To date, only particles with three or two quarks have been confirmed and only protons are stable. That is all baryons and mesons, except protons decay and disappear quickly.

 

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)