Download Introduction to Electricity

Introduction to
Electricity
Electric Charge and Static
Electricity

Law of electric
charges

like charges repel and
opposite charges
attract

Electric Force

force of attraction or
repulsion on a
charged particle

Electric Field

space around
charged object in
which another
charged object
experiences electric
force

Charge it

objects become
positively charged
when it loses
electrons
negatively charged
when gains electrons

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Friction

Conduction

happens when
electrons are “wiped”
from one object onto
another

electrons move from
one object to another
by direct contact

Induction

charges in an
uncharged metal
object are rearranged
without direct contact
with a charged object

Conservation of
Charge

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Detecting Charge

when an object is
charged, no charges
are created or
destroyed
electrons simply
move from one atom
to another
Electroscope –
uncharged = metal
leaves hang down;
charged = metal
leaves repel
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Electrical Conductor

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Electrical Insulator


material in which
charged can move
freely
most metals, salt
solution, graphite
material in which
charges cannot move
freely
plastic, rubber, glass,
wood, air

Static Electricity

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Electric Discharge

electric charge at rest
produced by friction
or induction
“static” = not moving
release of electricity
stored in a source
Electric Current and Electrical
Energy

Electrical Energy

energy of electric
charges

Electric Current

rate at which charges
pass through a given
point
measured in amperes
(A); in equations the
symbol is I

• Commanding
Electrons to Move This
electric field is created so quickly that all
electrons start moving through the wire at the
same instant. Think of the electric field as a
command to the electrons to charge ahead.

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Two Kinds of
Currents:
AC – Alternating
Current
DC – Direct Current

charges continually
shift from flowing in
one direction to
flowing in the reverse

charges always flow
in same direction

Voltage

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

potential difference
between two points
measured in volts (V)
amount of energy
released as a charge
moves between two
points in the path of a
current
higher voltage = more
energy released

Resistance





opposition presented
to the current by a
material or device
expressed in ohms
(Ω)
“electrical friction”
higher resistance =
lower the current
depends on object’s
material, thickness,
length, and
temperature
•Resistance and Temperature In general, the
resistance of metals increases as temperature
rises.

Superconductor

material with almost zero
resistance when cooled

Cells


change chemical or radiant energy
into electrical energy
batteries are one or more cells

allow charges to flow

part of cell through which charges
enter or exit

Electrolytes

Electrodes

Wet Cell

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Dry Cell

Thermocouple
liquid electrolytes
ex. car battery –
sulfuric acid

electrolytes are solid
or paste-like

converts thermal
energy into electrical
energy

Photocell


converts light energy
into electrical energy
ex. solar panel
Electrical Calculations

Ohm’s Law

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named after George Ohm,
1826
determined how resistance
and current affect voltage
increasing voltage increases
current
increasing resistance
decreases current
V = I x R or I = V/R
V – voltage, I –
current/amps, R – resistance

Electric Power

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Electrical Energy

rate at which electrical
energy is converted into
other forms of energy
power = voltage x current
P=VxI
measured in watts (W) or
kilowatts (kW)
power x time
E=Pxt
Electrical Circuits

Electrical Circuit

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complete path
through which a
charge can flow
three parts: energy
source, wires, a load
(light bulb, radio)
sometimes also
includes a switch

Open Circuit

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Closed Circuit

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circuit is broken;
electricity will not flow
“turned off”
circuit is complete
and electricity will flow
“turned on”

Series Circuit

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charge has only one
path through which it
can flow
if one element stop
working, none of the
elements can work

Parallel Circuit


two or more paths
through which
charges can flow
if one element stops
functioning, the rest
still operate

Fuse



Circuit Breaker

prevents current
overload in a circuit
“blowing a fuse” is
when a wire in the
center of the fuse
melts
switch that opens
when current is too
high

Grounding

transfer of excess
charge through a
conductor to Earth