Transcript Static Electricity

Static Electricity
Electricity & Magnetism
Static Electricity
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Matter is composed of small particles called
atoms.
The atom is composed of protons, neutrons,
and electrons.
Normally, atoms are neutral (no charge)
because they have the same number of protons
as electrons.
Some substances can gain and lose electrons
easily because of their properties.
Static Electricity
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When a balloon is
rubbed with a wool
cloth (friction), the
wool cloth loses some
of its electrons.
Because the wool cloth
now has more protons
than electrons, it is
positively charged.
The balloon has gained
electrons and is,
therefore, negatively
charged.
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By bringing the
negatively charged
balloon into contact
with positively
charged items, they
become attracted.
Law of Electrostatics
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This is an example of one
of the basic Laws of
Electrostatics: Unlike
charges attract each
other.
It also states that like
charges repel.
Example: If two negatively
charged balloons are
brought near each other,
they repel each other.
Static Electricity
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Electrons sometimes jump between
objects. When this happens we sometimes
hear a “crack” and, in darkness, see a
spark.
Producing Electric
Energy
Electricity & Magnetism
Magnets and Magnetism
An electric current flows when electrons
move from atom to atom through a
conductor.
 In 1820, Hans Oerstead, a Danish
physicist, discovered that electric current
passing through a wire produces a
magnetic field around the wire.
 If the wire is coiled around an iron ore an
electromagnet is produced.
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Producing Electric Energy
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Other methods of generating electric current
have been found, such as with chemical
energy.
The wet cell, a battery, consists of a copper
strip (positive electrode) and a zinc strip
(negative electrode) in a diluted acid solution.
The acid solution, known as an electrolyte, is
capable of conducting an electrical current.
Producing Electric Energy
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Electrons leave the copper strip,
giving it a positive charge. As the zinc
dissolves, it has surplus electrons,
giving it a negative charge.
Electrons flow from the zinc strip
through the conductor to the copper
strip.
The electrical current produced from
the flow of electrons can cause a
bulb to light.
Producing Electric Energy
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The current produced is called
direct current (D.C.).
Heat energy can also be used
to generate an electrical
current.
When set of dissimilar metal
strips (called thermopiles) are
heated, an electric current is
generated that flows through
the connecting wires.
Producing Electric Energy
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An instrument called the
ammeter measures electric
current.
Sunlight can also be used to
produce electricity.
Solar cells consist of
semiconductors made of silicon
crystals.
The sun’s energy can cause
electrons to flow between the
semiconductors, producing a
small current.
Producing Electric Energy
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A power plant generator consists of
electromagnets that are made to spin within
an armature, which consists of many coils of
wire.
The process begins with a turbine, which will
turn from the force of wind, moving water, or
heated water (steam).
Producing Electric Energy
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At the spinning of the
turbine and shaft cause
electromagnets to spin
within the armature.
This current is used to
supply the
electromagnets and to
supply electrical energy
for consumers.
The current generated is
called alternating
current (A.C.)
Complete Circuits
Electricity & Magnetism
Complete Circuits
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The electrical energy
produced by a generator
or battery can be made to
follow certain paths.
The flow of electrical
energy is called an
electrical current.
The electrons flow in a
metal conductor, such as
copper wire, is from the
negative to positive pole.
Complete Circuits
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The path taken by the electrical current is known
as a circuit.
When the pathway is unbroken and the current
flows from the source through the conductor and
back again, the circuit is said to be complete.
Complete Circuits
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When someone flips on a light
switch, the circuit is complete
and electrical current flows
through the light bulb,
producing light.
When someone pushes a
doorbell button the circuit is
complete and the bell rings.
The complete circuit is also
called a closed circuit
because there is no opening
or break in the path of
electron flow.
Complete Circuits
A switch allows one
to control the flow of
electrical current.
 When the switch is
open, or in the off
position, the current
cannot flow through
the conductors.
 This is called an open
circuit.
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Complete Circuits
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If the electric current completes a circuit without
servicing the device it was intended to operate, as when
two bare conductor wires come in contact with each
other, a “short circuit” results.
This causes the wire to heat up without operating the
electrical device.
Series and Parallel
Circuits
Electricity & Magnetism
Series and Parallel Circuits
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Electrical current can be
measured in several ways.
Electrons flow through a
conductor when there is a
surplus of electrons at one
pole and a deficit at the
other pole.
The electrical potential of the
two poles is different. This
difference is known as the
electromotive force (EMF), or
voltage.
Series and Parallel Circuits
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The instrument used to measure voltage is the
voltmeter.
The rate of flow of the electrical current is
measured in units called amperes (amps).
The ammeter is the instrument used to measure
amperage.
As the electrons move through the conductor, a
certain amount of opposition is known as
resistance and is measured in units called
ohms.
Series and Parallel Circuits
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Various factors affect the resistance of a
conductor:
 Type
of material
 Thickness of material
 Length of material
Series and Parallel Circuits
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A complete circuit can be set up
in two ways, a series or
parallel circuit.
In the series circuit the
electrons have only one path
through which they may flow.
When two bulbs are connected
in series with one dry cell, the
ammeter shows that the
strength of the current is less
when compared to a one bulb
circuit because the second bulb
acts as a resistor.
Series and Parallel Circuits
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When two bulbs are connected in parallel with
one dry cell, the ammeter indicates greater
amperage compared to the one bulb circuit.
This is because the current has more than one
path to follow so there is less resistance.
Magnets and
Magnetism
Electricity & Magnetism
Magnets and Magnetism
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Magnetic iron ore was
discovered by the Greeks
in a region once known as
Magnesia.
Natural magnets, called
lodestones, are composed
of the mineral magnetite.
Certain materials such as
iron (steel), nickel, and
cobalt are attracted to
magnets and can be
formed into magnets of
various shapes.
Magnets and Magnetism
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The domain theory of magnetism is based on the
concept of the magnetic field of individual atoms.
Certain elements, such as iron, can become
aligned.
The aligned clusters of atoms then form magnetic
domains within pieces of iron.
Magnets and Magnetism
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The attraction or
repulsion is strongest
at the ends, called
poles.
One end is the north
seeking pole (N) and
the other is the south
seeking pole (S).
When like poles are
brought together they
repel each other,
unlike poles attract
each other.
Magnets and Magnetism
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The magnetic field in the space around
a magnet is defined by the lines of
force.
The patterns of these invisible lines of
force can be seen when iron filings are
sprinkled around a magnet.
Magnets and Magnetism
The earth behaves as a huge magnet
and therefore has magnetic lines of force.
 It is these lines of force that align the north
end of a directional compass needle to
the magnetic north pole of the earth.
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Electromagnets
Electricity & Magnetism
Magnets and Magnetism
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In an unmagnetized piece of
iron the domains are randomly
oriented.
However, if the piece of iron is
placed next to a strong
magnet, many of the domains
will arrange themselves in line
with the magnetic field.
Electromagnets
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Electromagnets have three requirements:
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Electric current
Coiled, insulated wire
A soft iron bar
When a current flows through the coiled wire wrapped
around the bar (core), the bar and coiled wire act like a
magnet.
They can pick up objects and they have north and south
seeking poles.
Electromagnets
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For electromagnets, a
soft iron bar is used
because it magnetizes
easily and also loses its
magnetism easily.
An electromagnet will
continue to be a magnet
as long as the current
flows through the coiled
wire.
For this reason,
electromagnets are
called temporary
magnets.
Electromagnets
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When a current flows through
a wire, a magnetic field (lines
of force) occurs.
In an electromagnet the lines
of force occur around the soft
iron core and coiled wire.
The electric force of an
electromagnet can be made
stronger in two ways:
 By
increasing the number of
turns of coiled wire around
the core
 And/or by increasing the
amount of electric current
Electromagnets
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Doubling the number of turns of
wire or doubling the electric
current will double the
magnetic force of the
electromagnet.
The poles of the electromagnet
can be reversed by reversing
the wire connection at the
source of electricity.
Pole designation may be
determined by using a
compass.
Electromagnets
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Electromagnets are used in many objects:
 Telephones
 Telegraphs
 Radios
 Televisions
 Motors
 Doorbells
 Electrical
appliances