# Electric Current and Ohms Lawx - WHSFreshmanScience

Urban and Civil

Nov 15, 2013 (4 years and 7 months ago)

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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.