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Chapter 4 Magnetism and Electricity 4.1 MAGNETIC FORCES AND FIELDS MAGNET: an object that can exert a pull, of force, on a piece of iron. It can attract or repel an object without touching it. MAGNETIC FIELD: a region in space where magnetic effects can be detected. It is used to show how magnets exert forces on an objects. The stronger the magnet the larger the field. The earths magnetic field is millions of kilometers in diameter. MAGNETIC POLES The region on a magnet where the magnetic fields are the strongest, they are usually on the end of each magnet. NORTH POLE: the end of the magnet that is attracted northwards. SOUTH POLE: the end of the magnet that is attracted southwards. MAGNETIC LINES OF FORCE Lines that show the magnetic field. They are always drawn from the north pole to the south pole because this is the direction a compass needle would point when near a magnet. N S N S N S S N GEOMAGNETIC POLES The places in the earths magnetic field that are the most concentrated. They are not at the north pole or the south pole. Actually they are 1500km from the N pole and 2600km from the S pole. Draw figure 4.6 Label -geographic north and south pole -geomagnetic north and south -the bar magnet inside the earth 4.2 MAGNETS AND MAGNETISM MAGNETIC ELEMENTS: any material that can be magnetized, Iron, Cobalt, Nickel, and Gadolinium CAUSES OF MAGNETISM: more atoms are aligned in one direction than in any other direction. Therefore more electrons are moving in one direction, so the magnetic affects do not cancel each other out. PROPERTIES OF MAGNETS Can occur naturally as magnets, example: iron oxide Every magnet has two poles 1) a north pole which is attracted to the north pole 2) a south pole which is attracted to the south pole If 2 north poles are brought together they will repel If 2 south poles are brought together they will repel If a north and a south pole are brought together they will attract MAGNETIC DOMAIN: groups of aligned atoms or electrons. a) magnetized b) demagnetized PERMANENT MAGNET: materials that are able to stay magnetized for a long time. These magnets are able to lose their magnetism if the object is dropped or banged because this causes the domain to become disordered. 4.3 ELECTROMAGNETISM the magnetic field that is produced when an electric current is passed through a magnetic material ELECTROMAGNETS: a magnet that is only produced when an electric current flows through the material Used in doorbells, telephones, speakers etc; RIGHT-HAND-RULE: used to predict the magnetic lines of force around a current carrying wire. It states if you point your right thumb in the direction of current flowing in the wire, the curl of your fingers will indicate the direction of the magnetic lines of force around the wire. Wire with current coming out of the page Wire with current going into the page ELECTROMAGNETS There are 3 ways to increase the strength of a magnet 1. use a stronger electricity source to increase the current (bigger battery) 2. wrap more coils of copper wire around the object 3. use a larger metal core for the magnet 4.4 ELETRIC GENERATORS ELECTRIC GENERATORS: any device that can change electrical energy into mechanical energy - Generators produces electricity by moving a conductor through a magnetic field or by changing the magnetic field surrounding the conductor. Each procedure exerts a force on the electrons in the conductor and results in the electrons moving through it. A coil and magnet moving back and forth act as the generator of electricity because the movement of the magnet, changes the magnetic field around the coil. GALVANOMETER: is a device that can measure currents ALTERNATING CURRENT -current that can flow in both directions - it is produced in a generator and changes direction 120 times per second DIRECT CURRENT - current that can only flow in one direction - it is produced in a battery and only flows in one direction ELECTRIC MOTORS - electric motors change electrical energy into mechanical energy, therefore; they are opposite to electric generators RIGHT-HAND-RULE SELF TEST Predict the direction of the compass needle in the following examples 1. + 2. _ Current coming out of the page - 3. Current going into the page RIGHT-HAND-RULE SELF TEST Predict the direction of the compass needle in the following examples 1. + 2. Current coming out of the page _ - 3. Current going into the page Feb 27th, 2002 Name________________ Magnetism Quiz 1 Answer the questions in the space provided. 1. What is a magnet? 2. What are 2 materials that are naturally magnetic? 3. Draw a few lines of magnetic field around the following magnets. S N S NN N 4. Describe what a magnetic domain would look like in a piece of magnetized material. Feb 27th, 2002 Name________________ Magnetism Quiz 1 Answer the questions on a separate piece of paper 1. What is a magnet? 2. What are 2 materials that are naturally magnetic? 3. Draw a few lines of magnetic field around the following magnets S N S NN N 4. Describe what a magnetic domain would look like in a piece of magnetized material. Name________________ March 1st, 2002 Magnetism Quiz 2 Answer the questions in the space provided. 1. The current is flowing from the + to the -, using the Right-Hand-Rule, show the direction of magnetic field on the wire. + - 2. Name 2 ways to increase the strength of an electromagnet. 3. What is a permanent magnet 4. Name two ways to demagnetize a magnet. Feb 27th, 2002 Name________________ Magnetism Quiz 2 Answer the questions in the space provided. 1. The current is flowing from the + to the -, using the Right-Hand-Rule, show the direction of magnetic field on the wire. + 2. Name 2 ways to increase the strength of an electromagnet. 3. What is a permanent magnet? 4. Name two ways to demagnetize a magnet. -