Chapter 14.1

MAGNETS AND MAGNETIC FIELDS

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=Lj6c5ebi0a4

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.

Chapter 14.2

MAGNETISM FROM ELECTRIC CURRENTS

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

Chapter 14.3

ELECTRIC CURRENTS FROM MAGNETISM

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