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# BYU - PHY S 100 - Physical Science 100 Textbook Notes Week 2 - Class

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BYU - PHY S 100 - Physical Science 100 Textbook Notes Week 2 - Class

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Physical Science 100
Ch. 4: The Electromagnetic Interaction
Week 2

Some objects become "electrified" or "charged" when rubbed against other materials
Like gravity, the force from electrification (the electric force) is stronger at closer distances;
unlike gravity, it can repel as well as attract
Glass vs rubber: objects attracted to a rubber rod=positively charged, objects attracted to a glass
rod=negatively charged
Ben Franklin's electricity experiments: used Leyden jars to store and use static electricity,
showed the connection between lightning and electricity

4.1 The Electric Force Law
● de Coulomb found through an experiment a law that described the electric force  ○ He found that the force between charged bodies is proportional to the size of the  charge on them, while decreasing with the distance squared, just like the
gravitational force
● The electric force law: pairs of objects with similar charges repel each other and pairs  with dissimilar charges attract each other with forces, F, that obey Newton's Third Law.
The strength of F depends on the net charges, q and Q, of the objects and the distance, d,
between their centers, according to the relationship F=kQq/d^2
○  electric force constant (k): a number relating the strength pf the electric force to  the charges involved and their distance apart…just like the constant G in the law
of gravity, it must be measured experimentally (has a very large value instead of a
very small value)
○ A tiny amount of charge will generate the same amount of force created by a huge  amount of mass
4.2 The Electrical Model of Matter
● Franklin's model of electricity assumed matter had a charged fluid part embedded in an  oppositely charged, less mobile part. This hypothesis emerged as the better model.  ● J.J. Thomson began to study what the fluid was made of and how it was able to flow  1. See Fig. 4.5 (page 43) for Thomson's experiment that tore atoms apart and  examined the pieces that emerged  2. The glowing beam in the tube obeyed Newton's laws of motion, which proved  that electricity has mass  3. He decided that the atoms of gas in the tube were being broken into charged  fragments
■ The negative fragments had the same mass regardless of the type of gas,  but the positive fragments retained the mass properties of the original
gas…led to a model of the atom.
4. Franklin's "electrical fluid" was proven to be a stream of particles
5. Electron: the basic negative charge-carrying particle in an atom
● Robert Millikan devised an "oil-drop experiment" that isolated and measured the charge  on individual particles (see Fig. 4.6, page 44)  1. Coulomb: the unit of measure for charge. The amount of electric charge possessed  by a single electron or a proton is 1.6 x 10^-19 coulombs  2. Discovering the particle nature of an electron allowed for advanced electricity  research and modern inventions (light bulbs, computers, cameras, etc.)  ● Proton: a positively charged particle in atomic nuclei made up of 3 quarks  1. Carries the same exact charge as an electron, only with the opposite sign  ● Neutron: an uncharged particle in atomic nuclei made up of 3 quarks  1. Compromise the bulk of the mass of an atom  ● The structure of matter is so that protons are held more rigidly in place in solids than are  electrons  1. The less massive electrons accelerate more than the massive protons (second law  of motion); therefore, the electrons are the ones that break free and move (that is
what causes visible lightning)
2. The electrical model of matter:
3. All matter contains 2 kinds of electrically charged particles: positive protons and
negative electrons.  4. Electrons have little mass and can be quite mobile and transferrable from one  object to the other  5. Protons are held rigidly in place in solid materials
6. Objects that have equal numbers of protons and electrons are electrically neutral.
7. Objects with more electrons than protons are negatively charged
8. Objects with fewer electrons than protons are positively charged
9. The amount of extra charge of either kind is called the "charge of an object"

4.3 Electric Current
Even though electrons are mobile, they do not move through all materials with equal ease
● Insulator: a material that does not permit electrons to flow through it (i.e. rubbing  electrons onto a rubber rod that remain on its surface; therefore, rubber is a type of
insulator)
● Conductor: a material that allows electricity to flow through it (i.e. a copper rod)
● Electric current: electric charges flowing through a conductor

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##### Description: These notes cover week 2 of the PS 100 course.
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