UNIT 8. ELECTRICITY AND MAGNETISM (NATURAL SCIENCE)

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.