UNIT 8
WHAT IS ELECTRICITY?
·
Electrical
charges
Electricity begins
in atoms. Atoms are made up of protons and neutrons inside a nucleus and
electrons that move around them. Protons have positive electric charge and
electrons have negative electric charge. Neutons have no charge. If an object
has the same number of electrons and protons, it is electrically neutral.
However, electrons sometimes move easily from one object to another, so the
object is electrically charged.
·
Forces
between electrical charges
Electrically
charged objects attract or repel objects, depending on their charges.
·
Static
electricity
Storms are an
example of static electricity. Ice particles in the cloud move very fast and
rub together. The cloud charges negatively and the ground is positively
charged. If the electrical charge of the cloud is enough, it will meet the
positive charge of the ground and causes energy in form of light, heat and
sound.
·
Current
electricity
The movement of
electrons from one object to another creates electrical current. Some materials
like rubber or plastic are resistant to the movement of electrons but there are
others, that are good conductors. The electrical current travels through a
electrical circuit. Its parts are:
-
A power source (produces energy, like a battery)
-
Wires (transport electricity)
-
A switch (opens and closes the circuit)
-
A resistor or receptor (receives electricity and
transforms into another form of energy).
MAGENISTISM
A magnet is an object that
attracts metals and the ability to attract metals is magnetism. There are
natural and artificial magnets. Magnetite, for example, is a natural magnet but
most of magnets are artificial. Magnets c abe:
-
Permanent, they never lose their magnetism.
-
Induced or temporary , have a temporary magnetic
force.
All magnets have two poles: north
and south. If you break a magnet, both parts will have north and south
poles. If you hold a magnets it will
always point to the magnetic north pole. Two different poles attract, but two
equal poles, repel.
·
Magnetic field
The forcé around a
magnet is called magnetic field. We can´t see this field but we can see its
shape using iron filings. The magnetic field is stronger at the poles.
·
The Earth is a magnet
The Earth´s molten
iron core acts like a huge magnet. The magnetic field around the Earth deflects
(or changes the direction of) cosmic
rays and potects our atmosphere.
·
Compass
A compass is an
instrument used for navigation. The
needle og the compass is magnetised and points to the magnetic North pole. The
circle around the needle , called rose, is marked with cardinal points.
MAGNETS AND ELECTROMAGNETS
Magnetic materials are always
made of metal but ot all metals are attracted by magnets.
·
Electromagnets
They are objects
that act as magnets when an electrical current passes through them.
·
Magnets all around us
We use magnets
every day, for example, to listen to music through the headphones .
Electromagnets are used in motors, generators, etc. Many home appliances, like hairdryers,
transform electricity into mechanical energy.
In hospitals, magnetic resonance imaging is used to detect problems in
our organs. Magnets are also used
for separation and lifting heavy objects. In transport, some trains (like
Maglev) use magnetic levitation to move without touching the ground.