Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism, chemistry and thermal conductivity, and they also participate in gravitational, electromagnetic and weak interactions. Since an electron has charge, it has a surrounding electric field, and if that electron is moving relative to an observer, said observer will observe it to generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons radiate or absorb energy in the form of photons when they are accelerated.Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications such as tribology or frictional charging, electrolysis, electrochemistry, battery technologies, electronics, welding, cathode-ray tubes, photoelectricity, photovoltaic solar panels, electron microscopes, radiation therapy, lasers, gaseous ionization detectors and particle accelerators.
Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms. Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge 'electron' in 1891, and J. J. Thomson and his team of British physicists identified it as a particle in 1897 during the cathode-ray tube experiment. Electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere. The antiparticle of the electron is called the positron; it is identical to the electron except that it carries electrical charge of the opposite sign. When an electron collides with a positron, both particles can be annihilated, producing gamma ray photons.
In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons, which are believed to be fundamental or elementary particles. Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first-generation of fundamental particles. The second and third generation contain charged leptons, the muon and the tau, which are identical to the electron in charge, spin and interactions, but are more massive. Leptons differ from the other basic constituent of matter, the quarks, by their lack of strong interaction. All members of the lepton group are fermions, because they all have half-odd integer spin; the electron has spin 1/2.
The apparent paradox in classical physics of a point particle electron having intrinsic angular momentum and magnetic moment can be explained by the formation of virtual photons in the electric field generated by the electron. These photons can heuristically be thought of as causing the electron to shift about in a jittery fashion (known as zitterbewegung), which results in a net circular motion with precession. This motion produces both the spin and the magnetic moment of the electron. In atoms, this creation of virtual photons explains the Lamb shift observed in spectral lines. The Compton Wavelength shows that near elementary particles such as the electron, the uncertainty of the energy allows for the creation of virtual particles near the electron. This wavelength explains the "static" of virtual particles around elementary particles at a close distance.
At the end of its lifetime, a star with more than about 20 solar masses can undergo gravitational collapse to form a black hole. According to classical physics, these massive stellar objects exert a gravitational attraction that is strong enough to prevent anything, even electromagnetic radiation, from escaping past the Schwarzschild radius. However, quantum mechanical effects are believed to potentially allow the emission of Hawking radiation at this distance. Electrons (and positrons) are thought to be created at the event horizon of these stellar remnants.
Electrons are important in cathode-ray tubes, which have been extensively used as display devices in laboratory instruments, computer monitors and television sets. In a photomultiplier tube, every photon striking the photocathode initiates an avalanche of electrons that produces a detectable current pulse. Vacuum tubes use the flow of electrons to manipulate electrical signals, and they played a critical role in the development of electronics technology. However, they have been largely supplanted by solid-state devices such as the transistor.
P2-31: E/M OF ELECTRON APPARATUSLecture Demonstration Instructions Sheet.William J. Thompson, Determining e/m with a Bainbridge tube: Less data, more physics, AJP 58, 1019-1020 (1990).Lawrence A. Ferrari and Kenneth E. Jesse, Experiment to Measure e/mfor an Electron, TPT 34, 434-437 (1996).
All candidates for the B.S. and B.A. degrees must satisfy the course breadth requirements for the Undergraduate Studies Section of the College of Natural and Agricultural Sciences. In addition, a candidate must complete 70 quarter units of approved lower and a minimum of 57 units of upper division letter grade physics courses for the standard track, totaling a minimum of 127 quarter units of physics core requirements. Of these, 12 units are upper division elective classes, which focus on specific disciplines. Students are encouraged to become involved in research with a faculty mentor and write a Senior Thesis (Phys 195), which satisfies half of the senior advanced lab requirement (Phys 142). To graduate, a minimum grade point average of 2.0 (C) is necessary overall and in the upper-division classes taken for the major. A minimum of 180 units of academic work with a grade point average of 2.00 is required for graduation. Students who wish to take more than 216 units must receive permission from the associate dean.
However, the following alternative paths will satisfy the introductory physics requirement for the major. Please consult your physics faculty academic advisor before committing to an alternative path. Students who wish to change their major to physics may follow any of the paths below. If you have already started taking introductory physics, you do not need to start over with physics 41ABC.
This page shows a sample program for transfer students who enter UCR with all of introductory physics, including modern physics (PHYS41ABC or equivalently PHYS40ABCDE at UCR) and the lower-division math requirements (MATH 9ABC, 10AB, and 46 at UCR) already satisfied. Students develop a personalized program of courses through consultation with their faculty academic advisor.
The Standard Track is for students who primarily wish to work in industry in STEM fields or prepare for graduate school in Physics, Astronomy or Engineering. Students who wish to follow one of the specialty tracks (Biophysics, Physics Education, or Applied Physics and Engineering) should discuss the necessary modifications to their course plan with their faculty academic advisor.
This page shows a sample program for transfer students who enter UCR with part of introductory physics (PHYS41AB or equivalently PHYS40ABC at UCR) and all the lower-division math requirements (MATH 9ABC, 10AB, and 46 at UCR) satisfied, but have not yet taken modern physics (PHYS41C or equivalently PHYS40E at UCR). Students develop a personalized program of courses through consultation with their faculty academic advisor.
The Biophysics Track is designed to prepare students for careers or graduate school in biophysics, bioengineering, biomaterials, biotechnology or health-related fields. The requirements satisfy medical school admissions requirements. The track requires 95 lower division units (27 in Physics, 27 in Chemistry, 24 in Math, 13 in Biology, 4 in Computer Science) and a minimum of 49 upper division units, totaling 144 units. Relative to the Standard BS Physics track, 16 units of upper-division physics courses are replaced by 13 units of biology, 12 units of organic chemistry, and 2 upper-division biochemistry courses. There are 36 units of CNAS breadth. The CNAS Bio breadth requirement is met within the track requirements. The minimum total number of units is 177.
The Biophysics Track is designed to prepare students for careers in health-related fields or graduate school in biophysics, bioengineering, biomaterials, or biotechnology. This alternative track is for students who have completed Physics 2ABC. The lower division Physics requirement (24 units of Physics 41ABC) can be met by Physics 2ABC passed with a B+ letter grade in each course (15 units) and 12 units of additional upper division electives, 8 units in Physics and 4 units in any Science/Math/Engineering discipline. The following schedule has 197 units with 5 general electives. 2b1af7f3a8