Transcript Chapter 21: Electricity pp. 592-618

Electricity and Magnetism
Atomic Review
An atom consists of 3
particles:
 Protons-positively charged
 Neutrons-no charge
 Electrons-negatively
charged
What is Electricity?
• A form of energy caused
by moving electrons.
How charges act
 Like
charges repel
 Opposites charges attract
 Electrons flow from a
negatively charged area to a
positively charged area

Most objects are electrically
neutral
Static Electricity
Phenomena
 Lightning
 Leather
car seats
 Ben Franklin and the
kite.
 Sliding your feet on a rug
How are charges transferred?
 When
you rub two
substances together you
do work and thus you
add energy.
 This removes electrons
from one substance and
adds it to the other.
This creates IONS which are charged
particles.
Summary
The energy used to rub two
things together is the
energy that gets involved
in removing and
transferring electrons.
Electrical Charge
 Can
be
Transferred.
 It cannot be
created or
destroyed.
Conductors


A conductor allows charges to flow
easily
Some conductors are better than
others
Examples:
Copper
Iron
Insulators

An insulator prevents electric
charges from flowing easily
Examples:
Rubber
Cork
Wood
Plastic
Electric Current


Electric Current is the flow of
electrons through a conductor
There are two types of electric
current:
Alternating Current
Direct Current
Alternating Current


Changes direction at a regular rate
Most commonly used type of
electricity because it does not
create as much heat
Examples:
Appliances
Houses
Christmas lights
Direct Current


Always flows in one direction
Always flows from negative to
positive
Example:
Battery

Creates a lot of heat
What is a Battery?


A series of electrochemical cells
Two types:
A wet cell
A dry cell
Wet cell
 Electrolyte
is a liquid
Example:
Car battery
Dry cell

Electrolyte is a moist paste
Example:
AA battery
What is a circuit?


The path an electric current follows
Consists of four parts:
Source
Load
Wires

Switch
Current flows only through a closed
circuit
Diagrams

Source
Resistance

Lamp
Motor

Wire

Switch
What is a series circuit?


A circuit where current follows only
one path
If one light goes out, the whole
circuit goes out
Diagram of a Series Circuit
What is a parallel circuit?



Current follows more than one path
If one light goes out, the others
remain on.
Used in:
Homes
Schools
Buildings
Diagram of a Parallel Circuit
Circuit diagrams are a pictorial way of
showing circuits. Electricians and
engineers draw circuit diagrams to help
them design the actual circuits. Here is
an example of a
circuit.
What are volts?


Electromotive force (EMF) is the force
that moves electrons in a circuit.
A volt is the unit used to measure EMF.
What are amps?


The amount of current depends on
the number of electrons flowing in
the circuit.
An ampere (amp) is the unit used
to measure current.
What are ohms?



Resistance opposes the flow of
electrons in a circuit.
Resistance of a wire depends on
length, thickness, material, and
temperature.
An ohm is the unit used to measure
resistance.
Magnetism
Where do magnets come from?
Earth is a magnet
Iron can be made
into magnets
3 things stick to
magnets iron,
nickel, cobalt
Magnetic Pole




A pole is the area of the magnet
where the magnetic effect is the
strongest.
One pole of the magnet will always
point north this is the north pole.
The south pole will point south.
The north and south poles are
unlike and therefore attract.
Magnetism
Magnetic
Fields
Magnetic Fields
 Exist
in regions
surrounding magnets.
 Exerts a torque on a
compass needle. (Demo)
 Compass needles allow
us to map out magnetic
fields.
Magnetic
field lines
flow out of the north
pole and into the
south pole.
They are continuous
and never cross
The Earth itself is a
magnet!
Earth’s
magnetic field
causes compasses to
line up.
Magnetic north/south
pole is about 11º off
from geographic
north/south pole.
Why?

Scientists are not sure why the
Earth is a giant magnet but some
believe that it is due to the
circulation of molten metal (iron
and nickel) within the Earth’s core.
Oersted’s Discovery!
 The
presence of an
electric current in a wire
causes a torque in a
compass nearby.
 A current carrying wire
generates a magnetic
field.
.
 Electromagnetism
Electric Current
The flow of charge through a
material
The amount of charge that
passes through the wire in a
unit of time is the rate at
which the electric current
flows. The unit of current is
the ampere or amp.
An electric current produces
a magnetic field.
The direction of the
current determines the
direction of the
magnetic field in a
current carrying wire.
Cause
All
magnetism is
caused by the
movement of charges.
Electromagnet

An electromagnet is a strong
magnet that can be turned on and
off.
Increase strength





Increase the strength of a magnet
by:
Increasing the current
Increasing the number of loops of
wire to the solenoid.
Wind the coils of a solenoid closer
together.
Use stronger ferromagnetic material
for the core.