MAGNETS AND MAGNETIC FIELDS Chapter 14 1 MAGNETS

MAGNETS AND MAGNETIC FIELDS Chapter 14. 1

MAGNETS AND MAGNETIC FIELDS • Magnets got their name from the region of Magnesia, which is now part of modern-day Greece. • The first naturally occurring magnetic rock, called lodestones, were found in this region. • A lodestone is composed of an iron-based material called magnetite.

MAGNETS AND MAGNETIC FIELDS • Some substances, such as lodestones, are magnetic all the time. These types of magnets are called permanent magnets. • Other substances can be converted into permanent magnets. • For example, a piece of iron. • By striking it several times with a permanent magnet, it can become permanently magnetic. • Another method is by placing the iron near a strong magnet and eventually, the iron will become magnetic and remain that way even when the magnet is removed.

MAGNETS AND MAGNETIC FIELDS • So, we can take an nonmagnetic material and make it magnetic, but can we take the magnetism away? • Yes: we can either weaken the force or completely remove it. • Possible ways to do this include heat, or hammering the piece of iron. • https: //www. youtube. com/watch? v=Lj 6 c 5 ebi 0 a 4

MAGNETS AND MAGNETIC FIELDS • Scientists classify materials as either magnetically hard of magnetically soft. • Iron is a soft magnetic material. • Although iron is easily magnetized, it also tends to lose its magnetic properties easily. • Cobalt and Nickel are hard magnets • These materials are more difficult to magnetize. Once magnetized, they don’t lost their magnetism easily.

MAGNETS AND MAGNETIC FIELDS • Magnets exert magnetic forces on each other. • Figure 14 -3 • A magnet is lowered into a bucket of nails. As soon as a nail touches the magnet, the nail then acts as a magnet and attracts other nails. • The magnetic force involved is limited, however. • It is dependent upon the strength of the magnet as well as the distance from magnet to nail.

MAGNETS AND MAGNETIC FIELDS • Like poles repel, and opposite poles attract. • Magnetic pole – an area of a magnet where the magnetic force appears to be the strongest. • Magnets have a pair of poles, a north pole and south pole. • You cannot isolate a south magnetic pole from a north. If a magnet is cut, it will always have two different poles. • Two like poles, such as two south poles, repel each other. • Two unlike poles, such as a north and a south, attract one another

MAGNETS AND MAGNETIC FIELDS • Magnetic field – a region where a magnetic force can be detected. • When magnets repel or attract, it is due to the interaction of their magnetic fields.

MAGNETISM FROM ELECTRIC CURRENTS Chapter 14. 2

MAGNETISM FROM ELECTRIC CURRENTS • The magnetic field of a coil of wire resembles that of a bar magnet. • Solenoid – a long, wound coil of insulated wire. • The strength of a solenoid depends on the number of loops of wire and the amount of current in the wire.

MAGNETISM FROM ELECTRIC CURRENTS • The strength of a solenoid’s magnetic field can be increased by inserting a rod made of iron (or some other potentially magnetic metal) through the center of the coils. • The resulting device is called an electromagnet.

MAGNETISM FROM ELECTRIC CURRENTS • Domain – a microscopic magnetic region composed of a group of atos whose magnetic ields are aligned in a common direction.

MAGNETISM FROM ELECTRIC CURRENTS • Galvanometers are instruments that measure the amount of current in a circuit. • Electric motor – a device that converts electrical energy to mechanical energy.

CLASSWORK • Pg. 467, #1, 2 • Pg. 473, #3

ELECTRIC CURRENTS FROM MAGNETISM Chapter 14. 3

ELECTRIC CURRENTS FROM MAGNETISM • Electromagnetic induction – the production of a current in a conducting circuit by a change in the strength, position, or orientation of an external magnetic field. • In 1831, Michael Faraday discovered that a current can be produced by pushing a magnet through a coil of wire. • Faraday’s Law • An electric current can be produced in a circuit by a changing magnetic field.

ELECTRIC CURRENTS FROM MAGNETISM • Generators convert mechanical energy to electrical energy. • Generator – a device that uses electromagnetic induction to convert mechanical energy to electrical energy. • Alternating current – an electric current that changes direction at regular intervals; also called AC • The generators that produce the electrical energy that you use at home are alternating current generators.

ELECTRIC CURRENTS FROM MAGNETISM • One of the most common sources of mechanical energy is running water. • Dams harness the kinetic energy of water. As the water falls from small channels at the top of the dam to the base, it turns the blades of a turbine • The end result of this process is electrical energy. • Another example is burning coals. • This produces steam that eventually turns the blades of the turbines

ELECTRIC CURRENTS FROM MAGNETISM • Transformers – devices that can change one alternating-current voltage to a different alternating-current voltage. • Ex. Cylinders on power lines • Transformers have two circuits; primary and secondary. • These two circuits (wires) are coiled around opposite sides of a iron loop. • One wire is attached to a source of alternating current, such as a power outlet. The other wire is attached to an appliance, such as a lamp.

ELECTRIC CURRENTS FROM MAGNETISM • Step-up transformer – voltage across the secondary coil is greater than the voltage across the primary coil. • Step-down transformer – voltage across secondary coil is lower than the voltage across the primary coil

CLASSWORK • Pg. 480, #1, 2, 3 • Pg. 481, #1, 2, 3, 4, 7, 8, 9, 12, 15