# Electricity and Magnetism Notes - PAMS-ZAJAC

Ηλεκτρονική - Συσκευές

18 Οκτ 2013 (πριν από 4 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

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

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.