When the circuit is closed and the current flows through the circuit, it produces a magnetic field in the electromagnet. The hammer is attracted to the elctromagnet and hits the bell. The movement of the hammer breaks the circuit and the hammer returns to its original position. Then the cycle begins again.
MAGLEV
A magnetic levitation train uses electromagnets to levitate above its track.
The maglev has electromagnets in the base of the train.
The tracks have magnets which repel the electromagnets in the train.
The magnets above and in front of the train attract the magnets in the train, causing the train to move forward.
SPEAKERS AND MICROPHONES
Electric current travels through the coil of wire. This creates a magnetic field that switches on and off rapidly.
The magnetic field attracts the magnet, which is attached to the cone.
The cone vibrates rapidly, producing sound waves.
THERMAL ENERGY
The electric current produces a little thermal energy as it travels through a wire, but it produces a lot of thermal energy travelling through other substances (in an oven...).
A toaster uses thermal energy from electricity. Nick carson at en.wikipedia [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
CHEMICAL REACTIONS
Electrolysis is a chemical reaction produced when an electric current flows through a liquid solution of charged particles. We use elctrolysis in electroplating: coating a metal object with a thin layer of another metal.
The Earth has a magnetic field called the magnetosphere. It extends from the South Pole to the North Pole (it's as if the earth had a bar magnet in its centre). The North Pole is the South Pole of the Earth's magnetosphere.
Magnetosphere. By NASA (http://sec.gsfc.nasa.gov/popscise.jpg) [Public domain], via Wikimedia Commons
WHAT CAUSES THE MAGNETOSPHERE?
The centre of the Earth is made of liquid iron. This liquid moves slowly as the Earth rotates causing a magnetic field to form around the whole planet.
USING A COMPASS
A compass has a magnetised steel needle that is balanced inside a container. The north pole of the needle is painted red. It is attracted to the south pole of the magnetosphere: the magnetic north pole of the Earth. It will always point north.
Compass. By Evan-Amos (Own work) [Public domain], via Wikimedia Commons
WHY IS THE MAGNETOSPHERE IMPORTANT?
It deflects solar radiation from the Sun back into space. Radiation is harmful for plant and animal life on Earth.
It also helps us to navigate using a compass.
Bar magnets are permanent magnets, they can't be switched on and off, they always have a magnetic field. They have two poles: north (positively charged) and south (negatively charged). They attract metals such as iron, steel, cobalt and nickel. They also attract and repel other magnets.
Bar magnet. Photo taken by Aney, 2006-03-12, GFDL via Wikimedia
WHAT DOES A MAGNETIC FIELD LOOK LIKE?
We can see the magnetic field of a bar magnet using iron filings.
By Alexander Wilmer Duff [Public domain], via Wikimedia Commons
HOW DO WE REPRESENT MAGNETIC FIELDS?
We draw lines from the north pole to the south pole of the magnet. There are more lines and they're closer together near the poles because the magnetic field is stronger there.
WHAT HAPPENS WHEN TWO MAGNETS ATTRACT OR REPEL EACH OTHER?
Look at the pictures:
Two magnets repelling. By Geek3 [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Two magnets attracting. By Geek3 [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
HOW CAN WE IDENTIFY A MAGNET?
Magnets repel other magnets, but they don´t repel other substances.
Hans Christian Oersted discovered that electric current produces a magnetic force. Oersted saw that an electric circuit switched on made the compass needle move, but he couldn't explain the phenomenon.
André-Marie Ampere decided to study that phenomenon. He discovered the electron, which produces both, electricity and magnetism. But he named it the 'electrodynamic molecule'. Later, other scientists named it the electron.
By Ambrose Tardieu [Public domain], via Wikimedia Commons
Michael Faraday discovered that by moving a loop of wire over a magnet, an electric current was produced in the wire. He invented the 'electromagnetic rotary device', the basis for the first electric motor or dynamo.
By Probably albumen carte-de-visite by John Watkins [Public domain], via Wikimedia Commons
Faraday Disk Generator. By Émile Alglave [Public domain], via Wikimedia Commons
SEPARATING MIXTURES WITH MAGNETS
Electromagnets are made from a wire coiled around an iron rod. The wire is connected to a power source. When the electric current flows along the wire a magnetic field is generated. When you stop the circuit, the electromagnet is switched off. Electromagnets are used in recycling plants to separate iron and steel from plastic, glass or other metals.
Homemade electromagnet. By Gina Clifford (cobalt_grrl on Flickr) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 4.0-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/4.0-3.0-2.5-2.0-1.0)], via Wikimedia Commons
Aquí os dejo un modelo del examen que haremos el lunes. Si lo hacéis sin ver las soluciones podéis practicar y luego comprobar vuestros resultados con las soluciones que os doy en las otras imágenes.
Cuando lo tengáis hecho, aquí están las soluciones:
