Electricity and Magnetism Notes - PAMS-ZAJAC

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18 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

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Electricity and Magnetism Notes

Electric Charge


Protons and electrons both have the property of charge. Recall that protons are positive
and electrons are negative.


A force of attraction exists between things that have opposite charges.


A force of repulsi
on exists between things that have same charges.


Electric Field


An electric field

extends outward through space from every charged particle. As things
move toward each other the charge may move from one object to another.


The electric field is strongest

near the charged particle.


Static Electricity


Because electrons can move freely things can become either positively or negatively
charged. Charge is only being transferred from one object to another. This is called the
Law
of Conservation of Charge
.


Static electricity



is the buildup of electric charges on an object.


Methods of Charging


Friction


when two objects are rubbed together. Example: balloon on your hair.


Conduction


the direct contact of objects. Example: plugging something in.


Condu
ctors


allow electricity to go through easily


Insulators



do not allow it to move through.


Induction


the jumping of electricity from one object to another. Example: a negatively
charged rubber rod can pick up tiny pieces of paper.



Electric discharg
e



the

loss of static electricity as

electric charges move off

an object. Sometimes

slow and quiet, or rapid

with a spark of light, shock,

or crackle of noise.

Example: lightning or a

simple static shock


Circuits


A circuit


is formed when a wire is co
nnected to the terminals of a source forming a
complete path.


Electric current


the
amount of charge that passes a given point

per unit of time.


The symbol for current is I


Things to know…


Georg Simon Ohm

established the relationship between electric cur
rent and potential
difference. Ex. 8 v battery vs 4 v battery.


Resistance



R
opposition to the flow of electric charge

(example: copper low: iron high)
The unit to measure resistance is the ohm


Ohm’s law



the current in a wire is equal to the voltage d
ivided by resistance




I = V/R

Superconductor


Superconductor


low temperatures, resistance is zero. Must be kept extremely cold.


A phenomenon observed in several metals. When these materials are cooled to
temperatures near absolute zero, using liquid n
itrogen, they have no electrical resistance.
This means they can carry large amounts of electrical current for long periods of time without
losing energy as heat.


Superconducting loops of wire have been shown to carry electrical currents for several year
s
with no measurable loss

Another property of a superconductor is that magnetic fields can't penetrate it. It has
implications for making high speed, magnetically
-
levitated trains… kinda neat huh…


Current direction


DC (direct current
)


electrons alway
s flow in the same direction. Example: batteries


AC (alternating current)

electrons move back and forth, reversing direction regularly.
(example: current in home changes direction every second 120x)


Types of
Circuits


Electric circuit



consists of a sour
ce of energy; a load; wires, and a switch.


Sources:

battery, thermocouple, photocell, or electric generator


Load


uses the electricity


Series vs Parallel


Series circuit



only one path to take; if any part goes out the whole thing goes out.
Example: ol
d Christmas lights


Parallel circuit



separate paths. Example: circuits in homes.


Fuses


protect against too much current flow


Circuit breakers



like fuses but do not burn out.


Power


Electric Power



a measure of the rate at which electricity does work

or provides energy.
Measured in watts.


Power

= voltage x current


Energy

= power x time


Electric Safety


Never handle when wet or near water


Never run wires under carpet


Never overload circuits


Repair worn out wires


Put nothing in electric sockets that do
es not belong


Never go by fallen wires or power lines


In lightning storms get down to the ground by crouching down low and stay away from trees.


Safest spot in a lightning storm is inside a car.