Chapter 8 Magnetism and Its Uses Section 1: Magnetism Section 2: Electricity and Magnetism Section 3: Producing Electric Current
Section 1: Magnetism Standard 6: Demonstrate an understanding of the nature, conservation, and transformation of energy. Indicators: 6.11 Objectives: Explain how a magnet exerts a force. Describe the properties of temporary and permanent magnets. Explain why some materials are magnetic and some are not.
Magnetite Magnetite is a mineral that is naturally magnetic and it was discovered more than 2,000 years ago by the Greeks.
Magnetism Magnetism - refers to the properties and interactions of magnets.
Magnets Magnets exert a force on each other. Force: magnets either attract or repel depending on which ends are close. Force increases as magnets move closer and decreases as they move apart.
Magnetic Field Magnetic field - exerts a force on other magnets and objects made of magnetic materials. Magnetic field is strongest closer to the magnet and weaker further away.
Magnetic Poles Magnetic poles - where the magnetic force exerted by the magnet is the strongest. All magnets have 2 poles: north and south. North and south poles are at the opposite ends for a bar magnet.
Magnetic Poles Magnetic field lines always connect the north pole to the south pole of a magnet.
How Magnets Interact Like ends (N-N or S-S) will repel while unlike ends (N-S) attract to each other. When two magnets are brought close to each other, their magnetic fields combine to produce a new magnetic field.
Earth s Magnetic Field A compass determines direction because the north pole of the compass needle points towards the south magnetic pole (which is actually geographic north).
Section 2: Electricity and Magnetism Standard 6: Demonstrate an understanding of the nature, conservation, and transformation of energy. Indicators: 6.11 Objectives: Describe the magnetic field produced by an electric current. Explain how an electromagnet produces a magnetic field. Describe how electromagnets are used. Describe how an electric motor operates.
Electric Current and Magnetism Electric current (moving charges) produce a magnetic field around a wire.
Electric Current and Magnetism Direction of the magnetic field around a wire depends on the direction of the current through the wire.
Electromagnets Electromagnet - temporary magnet made by wrapping a wire coil carrying a current around an iron core. Iron core becomes magnetized.
Electromagnets Electromagnet has a north pole on one end and a south pole on the other end. An electromagnet will attract magnetic materials and be attracted or repelled by other magnets.
Electromagnets Magnetic field increases by: Adding more coils around the electromagnet Adding a larger core Increasing current in the coil
Electromagnets Electromagnets are temporary magnets because the magnetic field is present only when current is flowing through the wires.
Electromagnets The forces exerted on an electromagnet by another magnet can be used to make the electromagnet rotate. Poles of an electromagnet are repelled by like poles on a permanent magnet and attracted to unlike poles on permanent magnet.
Electric Motors Electric motor - device that changes electrical energy into mechanical energy. ex) any appliance that moves Motors contain an electromagnet called an armature.
Electric Motors When an electric current runs through the wire in the armature it becomes magnetized. The armature spins because other magnets in the motor push and pull it.
Steps to Making a Motor Spin Step 1: Current flows when brushes and commutator come in contact. This causes the armature to rotate because of the magnetic force between the two magnets.
Steps to Making a Motor Spin Step 2: Commutator and brushes are no longer in contact no current. Armature continues spinning because of inertia.
Steps to Making a Motor Spin Step 3: Armature is pushed by the permanent magnet because like ends repel. Step 4: Armature is pulled by the permanent magnet because opposite ends attract.
Section 3: Producing Electric Current Standard 6: Demonstrate an understanding of the nature, conservation, and transformation of energy. Indicators: 6.10, 6.11 Objectives: Define electromagnetic induction. Describe how a generator produces an electric current. Distinguish between alternating current and direct current.
Electromagnetic Induction Electromagnetic induction generation of a current by changing a magnetic field. This can occur when a wire moves relative to a magnetic field causing an electric current to be produced.
Generators Generators - use electromagnetic induction to transform mechanical energy into electrical energy. Turning handle on generator (mechanical E) coil rotates producing current (electric E).
Generators A generator is an electric motor working in reverse. Generators change mechanical energy into electrical energy.
Generators In a generators the coil keeps rotating which causes current to change direction twice with each revolution (1 complete turn of the handle).
Generators Rotation rate of the handle influences the frequency that current changes direction.
Generating Electricity for the Home Electrical energy comes from a power plant with large generators. Current in a power plant generator is produced as the magnet rotates around a stationary coil.
Generating Electricity for the Home The rotating magnets are connected to a turbine which is a large wheel that rotates when pushed by water, wind, or steam.
Electric Motors and Generators Both electric motors and generators use magnets to produce energy conversions between electrical and mechanical energy.
Direct and Alternating Current Current produced by a battery is different than the current from an electric generator.
Direct and Alternating Current Direct current (DC) - flows only in one direction through a wire. ex) battery (neg. terminal pos. terminal) Alternating current (AC) - reverses the direction of the current in a regular pattern. Ex) generators produce AC