Download Chapter 36 Summary – Magnetism

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Chapter 34 Summary
Electric charge comes from the electric forces between the positively charged
protons and negatively charged electrons. The flow of charge is called electric current
and is measured in amperes (amps). The symbol is I and the abbreviation for the units is
A. A difference in electric pressure at both ends of a conductor causes charges to flow.
The source of this constant potential difference is called a voltage source and is
measured in volts, abbreviated v. Since protons are trapped in the nucleus, the electrons
are the moving charges. When charges are not flowing, the net charge in the wire is
zero. When charges are flowing the net charge in the wire is zero because for every one
charge that enters one side, another charge leaves the other side and the total number of
protons and neutrons doesn’t change. DTE supplies power to the outlets in your wall
with a potential difference of 120 volts and an alternating frequency of 60 hertz.
Resistance is the opposition to current flow. It’s symbol is R and the units are ohms,
abbreviated Ω. Resistance basically depends on 3 things. Thicker, shorter, cooler wires
have less resistance which will allow more current to flow. When getting shocked, high
voltage is painful and can be deadly, but current is much more dangerous. As little as
0.07 A can kill you. There are 2 types of flow for current: direct current (DC) and
alternating current (AC). DC flows in one direction, is more portable to generate, but
has a finite amount of energy. Current switches direction for AC, is easier to
continually produce because we don’t have to supply any electrons, just move them, but
is harder to produce in a portable package. Electric power is calculated by multiplying
current and voltage. The symbol is P and the units are watts (W). Because our house
uses so much power, we use bigger units for power: kilowatts (kW). To calculate the
energy we use, multiply power and time (in hours). We are charged for energy in
kilowatt hours (kWh).