NASA-Threads
Electricity and Magnetism
Lesson 11: Atoms and Molecules
Lesson 11: Atoms and Molecules
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Review electricity (referring back to the example of the flow of electrons from a battery
discussed in the previous lecture)
Definition of insulators, conductors, semi-conductor (examples)
Review the Bohr model of a copper atom
Discuss what makes a good conductor, insulator, semi-conductor
Solve at least one in-class exercise using molar calculations
Electricity – the movement of charge (usually electrons).
Electricity can travel through some materials better than others.
Good conductors: gold, silver, aluminum, copper…
Poor conductors (Insulators): glass, plastic, rubber, wood, …
Semi conductors: modern materials designed to conduct only under certain conditions.
Transistors, LEDs, amplifiers.
The ability of a material to conduct electricity (for electrons to flow through the material)
depends on the atomic structure.
Lightweight electrons whiz about the nucleus. (We think of them as being in shells.)
Valence electrons in outer shell influence conductivity.
It is easy for copper to let the 4s1 electron go, so copper is
a good conductor.
Insulators hold onto their electrons more tightly
due to their electron configuration.
NASA-Threads
Electricity and Magnetism
Lesson 11: Atoms and Molecules
If you were talking with someone in China on the phone, your voice would cause the
diaphragm in the microphone to move which would induce electron motion. Would an
electron that you just caused to move in the microphone somehow get to China in a fraction
of a second? (Assuming a telephone line was stretched from here to China)
Flow of electricity through a copper wire:
The actual path that electrons take is scattered mostly due to atoms vibrating due to
temperature.
NASA-Threads
Electricity and Magnetism
Lesson 11: Atoms and Molecules
How many electrons are we talking about?
Homework
Assume a signal is induced on a transmission line. The signal travels at 0.7x the Speed of
Light. How long will it take to get from Dallas to Beijing?