Electric Current and Ohms Lawx - WHSFreshmanScience

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15 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Electricity: The Mouse and Cheese
Analogy


All matter is made up of positive
charges and negative charges.


The
positives have mass and are not usually
free to move.


The
negatives have no mass and are free to
move through some materials (conductors).

Mouse and Cheese Analogy


Negative

charges are attracted to
positive

charges the same way mice are
attracted to cheese.


Any time there is a natural attraction between two
things we can use it to make the objects do work.


The
negative

charges (mice) will gladly do work in
order to get to the
positive

charges (cheese).

Electric Current


Continuous flow of electric charge.


SI unit of electric current is the
AMPERE

(A) or amp.


1 amp = 1 coulomb per second.


Two types of electric current:


Direct Current (DC)


Alternating Current (AC)

Mouse and Cheese Analogy


Current:


The number of charges (mice) passing a
point per second. The rate of flow of
charges.

Direct Current


DC


Charges flow in
one direction.


Most battery
operated items use
DC.

http://www.geocities.com/capecanaveral/hall/6645/electmag/electricmotor.htm

Alternating Current


Flow of electric charge that regularly
reverses its direction.

Most electric current at
home and school.

Dotted lines are from AC

Conductor and Insulator


Electrical Conductor


Material through which charge
can flow easily.


Copper and Silver


Electrical Insulator


Coating around a wire that
controls the current and keeps it
where its needed.


Wood, plastic, air


Rubber


Insulating Material

(plastic)

Conducting Wire

(copper)

Superconductor


Material that
has almost
zero resistance
when cooled to
low
temperatures.


Best superconductors
must be cooled to
138K.

Resistance


Opposition to the flow of charges in
a material.


SI unit of resistance is ohm (
Ω
).


Four factors affect the resistance in
a wire:


Material type


Thickness


Length


Temperature

Mouse and Cheese Analogy


Resistance:


The opposition to the flow of charge.


Any
appliance that asks the charge (mouse) to
do work will slow it down.

Voltage


The difference of electrical
potential between two points of an
electrical circuit.


Also called the potential difference.


SI unit for voltage is a
VOLT


One volt = one joule per coulomb


Voltage:


The amount of work that each charge
(mouse) will do as it goes through
the circuit.


Can
also be thought of as

the amount
of push on the

charges
or how hungry the

mice
are.

Mouse and Cheese Analogy

Voltage Sources


Three common voltage sources:


Battery


Solar Cell


Generator

Battery


Device that converts chemical
energy to electrical energy


Ohm’s Law


Georg Ohm (1789
-
1854)


Found a relationship between voltage, current,
and resistance.


Ohm’s Law:


The voltage (V) in a circuit equals the product
of the current (I) and the resistance (R).



V = I x R


I =
V


R =
V








R



I

ELECTRICAL CIRCUITS

Chapter 20.3

Circuit Diagrams


Use symbols to represent parts of
a circuit.


Include:


Sources of electrical
energy


Devices that are run by electrical
energy

TYPES OF
CIRCUITS

Series Circuits


Charge has only
ONE

path through
which it can flow.


If
one

element stops functioning in a
series circuit,
NONE

of the elements
can operate.


The bulbs in a circuit are a source of
resistance. The more bulbs, the more
resistance.

Parallel Circuit


Charge has
TWO OR MORE
paths through which the
charge can flow.


If one element stops
functioning, the rest
of the elements can still
operate.