Download Unit 9: Energy, electricity and magnetism

Unit 9: Energy, electricity and
magnetism
Natural science
Electricity
● Electrical charges
● Electrical currents
● Electrical energy
Electrical charges and static electricity
Materials can receive electrical charges. A charge that objects receive under
certain conditions is static electricity:
● Combing your hair with a plastic comb
● Rubbing a glass or plastic object with a wool cloth
● Rub a balloon against your hair
These objects become positively or negatively electrically charged.
● Opposite charges (positive and negative) attract each other.
● Same charges (positive and positive / negative and negative) repel each other.
Electrical currents are the transfer
Electrical energy is associated with
of an electrical charge through objects.
This only works when the objects have
opposite electrical charges. For example:
electrical currents. Many of the machines
we use need electrical energy.
Storm clouds and Earth’s surface have
opposite electrical charges, so electrical
currents can jump from one to the other
through the air.
● lightening
Each end of a battery has an opposite
electrical charge. When they are
connected with a metal cable the charge
moves from one pole to the other.
Can produce changes in matter and can
be transformed into other types of energy.
● Light bulbs are transferred into
luminous energy
● Irons are transferred into thermal
energy
● Motors are transferred into kinetic
energy
Conductive materials
Materials and
electrical
currents
Electrical currents are produced
when a charge is moving from
one object to another, along a
material that allows it to move.
Electrical conductors are things that
allow currents to pass through them.
Metals are good conductors
● copper
Some non-metallic materials are also
good conductors
● Graphite and salt water
Insulating materials
Electrical insulators are things that do not
allow currents to pass through them.
● Wood, plastic and rubber
Electrical circuits are groups of elements that allow electrical currents to flow.
Components:
Generators transform transform different energy into electrical energy and produce currents.
● Batteries transform chemical reactions into electrical energy
● Alternators, like windmills and hydraulic turbines, transform mechanical energy into
electrical.
● Solar panels transform luminous energy into electrical using sunlight
Conducting cables transport currents from the generator to the receptor. Usually insulated to
avoid accidents and loss of current.
Switches are used to tu1rn currents on and off by stopping and allowing it to pass.
Receptors use the electrical energy that has been transported to them.
● Light bulbs - electrical into light
● Ovens - electrical into heat
● Electric motors - electrical into movement
Magnetism
Magnetism is the property allowing them to attract
or repel other objects.
Magnets are objects that have metal in their
composition and are able to attract other objects
that contain metal.
Magnets and their characteristics
All magnets have a magnetic field and two opposite poles, which attract, and two
like poles, which repel.
Magnetite is a naturally occurring mineral with magnetic properties. Magnets can
also be produced artificially from some metals (iron, cobalt, nickel and neodymium).
Poles: two areas usually at opposite end of the magnet, called north and south.
Magnets with one pole do not exist and if you cut a magnet in half each half
becomes a new magnet with two poles.
Magnetic fields: the influence magnets have on space around them. The closer a
magnet gets to a metallic objects the more intensely it starts to attract the object.
Earth’s
magnetism
Earth’s center is a mixture of metals:
mainly iron and nickel, which have
magnetic properties.
This makes Earth like a giant magnet,
having a magnetic north and south
pole which create a magnetic field.
Earth’s magnetic poles do not
coincide with geographical poles.
Uses of magnetism:
Compasses contain a small magnetic
needle which detects Earth’s magnetic
field and allows us to find direction.
Electrical equipment contain materials
with magnetic properties which allow us
to store data.
● Credit cards, computers, and hard
drives
Many other appliances use magnets to
keep them closed, hold things in place or
are used in toys.
● Locks, bags, fridges, suitcases
Magnets are also found with electricity in
generators, electrical motors, speakers
and microphones.
Electromagnetism
Is the use of electricity and magnetism, they are related.
Electrical currents can generate a magnetic field and
magnets can generate an electrical current.
Electromagnets
If we wrap a conducting wire around an
iron bar and pass an electrical current
through it, the iron bar will attract metal
objects and turn into an electromagnet.
If we switch off the current, the magnetic
properties also stop. Electromagnets are
temporary magnets.
Uses: doorbells, some car brakes and
clutches, machines that separate metallic
residue in recycling plants
Electromagnetic generators
Are alternators. They use magnetism to
generate electricity.
If we put a magnet near a coiled
conducting wire, the electromagnetic field
of the magnet will generate a current in the
wire, which is stronger if the magnet is
more powerful.
Ammeters are machines that measure
electrical current.
Uses: Power stations. Kinetic energy of
water, wind or water vapour is used to
move magnets that generates electricity.