* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Magnetic Field
Induction heater wikipedia , lookup
Electrostatics wikipedia , lookup
Insulator (electricity) wikipedia , lookup
Maxwell's equations wikipedia , lookup
High voltage wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Wireless power transfer wikipedia , lookup
Magnetic nanoparticles wikipedia , lookup
Friction-plate electromagnetic couplings wikipedia , lookup
Magnetic field wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Magnetic monopole wikipedia , lookup
Electromotive force wikipedia , lookup
Electromagnetism wikipedia , lookup
Electric current wikipedia , lookup
Electrical injury wikipedia , lookup
History of electrochemistry wikipedia , lookup
Lorentz force wikipedia , lookup
Electricity wikipedia , lookup
Hall effect wikipedia , lookup
Alternating current wikipedia , lookup
Faraday paradox wikipedia , lookup
Superconductivity wikipedia , lookup
Magnetoreception wikipedia , lookup
Scanning SQUID microscope wikipedia , lookup
Magnetohydrodynamics wikipedia , lookup
Magnetic core wikipedia , lookup
Multiferroics wikipedia , lookup
Electric machine wikipedia , lookup
Eddy current wikipedia , lookup
Magnetochemistry wikipedia , lookup
Force between magnets wikipedia , lookup
Superconducting magnet wikipedia , lookup
• When you finish turn to page 224 and begin reading about magnetism Chapter 8: Magnetism • Magnetism – Natural Magnets • Electricity and Magnetism – Electromagnets • Using and Producing Electricity – Generators and Motors • Production and Distribution of Electricity – Transformers Early Uses • Thousands of years ago, people noticed that a mineral called magnetite attracted other pieces of magnetite and bits of iron. • They discovered that when they rubbed small pieces of iron with magnetite, the iron began to act like magnetite. • When these pieces were free to turn, one end pointed north. Lodestone use for navigation. Magnets • Magnets attract objects made of iron or steel, such as nails and paper clips. • Magnets also can attract or repel other magnets. • Every magnet has two ends, or poles. • One end is called the north pole and the other is the south pole. Magnets • Two north poles or two south poles repel each other. Like Repel • North and south magnetic poles are attracted to each other. Unlike Attract The Magnetic Field • Where the magnetic field lines are close together, the field is strong. • Field lines that curve toward each other show attraction. • Field lines that curve away from each other show repulsion. Making Magnetic Fields • A magnet is surrounded by a magnetic field that enables the magnet to exert a magnetic force. • A moving electric charge creates a magnetic field. Making Magnetic Fields • Inside every magnet are moving charges. • All atoms contain negatively charged particles called electrons. • Not only do these electrons swarm around the nucleus of an atom, they also spin. Making Magnetic Fields • Because of its movement, each electron produces a magnetic field. • A group of atoms, with their fields pointing in the same direction, is called a magnetic domain. • Normally, these domains are oriented randomly and their magnetic fields cancel each other. • When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together. Making Magnetic Fields • Microscopic sections of iron and steel act as tiny magnets. • Normally, these domains are oriented randomly and their magnetic fields cancel each other. Making Magnetic Fields • When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together. Earth's Magnetic Field • The shape of Earth's magnetic field is similar to that of a huge bar magnet tilted about 11º from Earth's geographic north and south poles. The Compass • A compass needle is a small bar magnet with a north and south magnetic pole. • In a magnetic field, a compass needle rotates until it is aligned with the magnetic field line at its location. The Compass • Earth's magnetic field also causes a compass needle to rotate. • The north pole of the compass needle points toward Earth's magnetic pole that is in the north. • The magnetic pole in the north is actually a magnetic south pole. Making Magnetic Fields • Because of its movement, each electron produces a magnetic field. • A group of atoms, with their fields pointing in the same direction, is called a magnetic domain. • Normally, these domains are oriented randomly and their magnetic fields cancel each other. • When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together. Making Magnetic Fields • When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together. Current Can Make a Magnet • Magnetic fields are produced by moving electric charges. • When electric current flows in a wire, electric charges move in the wire. • As a result, a wire that contains an electric current also is surrounded by a magnetic field. Electromagnets • A current-carrying wire wrapped around an iron core is called an electromagnet. • An electric doorbell uses an electromagnet. • By changing the current, the strength and direction of the magnetic field of an electromagnet can be change. Using Electromagnets • The magnetic field of an electromagnet is turned on or off when the electric current is turned on or off. • By changing the current, the strength and direction of the magnetic field of an electromagnet can be change. Solenoid and Electromagnets Wire coils around iron rod Battery Iron Using Electromagnets • An electric doorbell uses an electromagnet. Galvanometer page 234-235 S N N S S Current Magnets Push and Pull Currents • Current-carrying wires produce a magnetic field. • This magnetic field behaves the same way as the magnetic field that a magnet produces. Magnets Push and Pull Currents • Two currentcarrying wires can attract each other as if they were two magnets. Electric Motor • Magnetic field like the one shown will push a currentcarrying wire upward. • Any device that converts electric energy into kinetic energy is a motor. Electric Motor • To keep a motor running, the current-carrying wire is formed into a loop so the magnetic field can force the wire to spin continually. Using Magnets to Create Current • If a wire is pulled through a magnetic field, the electrons in the wire also move downward. • The magnetic field exerts a force on the moving electrons, causing them to move along the wire. Using Magnets to Create Current • A device called a generator uses a magnetic field to turn motion into electricity. • Electric motors and electric generators both involve conversions between electric energy and kinetic energy. • When a wire is made to move through a magnetic field, an electric current is produced in the wire. • In a generator, kinetic energy is changed into electric energy. The Magnetic Field • Where the magnetic field lines are close together, the field is strong. • Field lines that curve toward each other show attraction. • Field lines that curve away from each other show repulsion. Making Magnetic Fields • When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together. Solenoid and Electromagnets Wire coils around iron rod Battery Iron Electric Motor • Magnetic field like the one shown will push a currentcarrying wire upward. • Any device that converts electric energy into kinetic energy is a motor. Using Magnets to Create Current • If a wire is pulled through a magnetic field, the electrons in the wire also move downward. • The magnetic field exerts a force on the moving electrons, causing them to move along the wire. Electric Generators • In a generator, an energy source spins a wire loop in a magnetic field. • Every half turn, the current will reverse direction. Electric Generators • This causes the current to alternate from positive to negative. • Such a current is called an alternating current (AC). • In the United States, electric current change from positive to negative to positive to positive 60 times each seconds. Types of Current • In a direct current (DC) electrons flow in one direction. Wet cells and dry cells produce DC current. • In an alternating current, electrons change their direction of movement many times each second. • Some generators are built to produce direct current instead of alternating current. Power Plants • Electric generators produce almost all of the electric energy used all over the world. • Different energy sources are used to provide the kinetic energy to rotate coils of wire in a magnetic field. • Burning fuels • Coal, Natural Gas • Moving Fluid • hydroelectric, wind turbines • Nuclear Energy Power Plants • Coal-burning power plants are the most common. • This picture is deceiving. • Problems • Dirty to mine • Dirty to burn • We will run out • Global Warming Making, Distributing, Using Electrical Energy Voltage • Voltage is a measure of how much energy the electric charges in a current are carrying. • Electrical Power is generated at a voltage of about 2,400 Volts. • Electrical Power is used at a voltage of about 240 Volts • The electric transmission lines transmit electric energy at a high voltage of about 230,000V. • Device are needed to increase and reduce the voltage. Changing Voltage • A transformer is a device that changes the voltage of an alternating current with little loss of energy. • Transformers are used to increase the voltage before transmitting an electric current through the power lines. Step Up Transformer • Other transformers are used to decrease the voltage to the level needed for home or industrial use. Step Down Transformer Changing Voltage Primary Secondary • A transformer has two coils of wire wrapped around an iron core. • One coil is connected to an alternating current source. 2 Primary The Transformer Ratio Secondary • Whether a transformer increases or decreases the input voltage depends on the number of coils on each side of the transformer. The Transformer Ratio • In a transformer the voltage is greater on the side with more coils. • If the number of coils on the input side is less than the number on the output side, the voltage is increased. • If the number of coils on the input side is more than the number on the output side, the voltage is decreased. Summary of E&M Principle Application A current moving in a wire produces a magnetic field around the wire Solenoid, electromagnet, doorbell, door locks, automatic controls The magnetic field of a permanent magnet will exert a force on the magnetic field around a current carrying wire. Galvanometer- a device for measuring electric current. Electric motor Stereo Speaker A wire moving through the magnetic field of a permanent magnet will produce an electric current in the wire. Generator A changing magnetic field will “induce” a current in a stationary wire. Transformer Schedule Date Activity Monday 2/4 Review/Electrical Generators Tuesday 2/5 Faraday Video Wednesday 2/6 Magnetism Lab Thursday 2/7 Transformers and Electrical Distribution Friday 2/8 Transformer Problems Monday 2/11 Notetaking worksheet Tuesday 2/12 Chapter Review Wednesday 2/13 Chapter 8 Test Wednesday 2/20 DUKE Energy Field Trip Assignment 8:00 – 10:30 Step Up Transformer Step Down Transformer Input Output Step Up/Step Down Transformers V input # input coils = V output # output coils Electric Power production and distribution Page 260 Produce Heat 60% Step Up Transformer Heat to Steam 90% High Voltage wires Steam to Rotation 75% Step Down Transformer Distribution Lines Rotation to Electricity 95% Step Down Transformer Household Usage Connecting Electricity and Magnetism • Electric charges and magnets are related to each other. • Moving electric charges produce magnetic field. • A moving magnetic field make electric charges move. Definitions 1 • Solenoid – a coil of wire carrying an electric current which produces a magnetic field. • Electromagnet- a coil of wire (solenoid) with an iron core which produces a stronger magnetic field. • Applications – doorbells, actuators of all sorts Definition 2 • Galvanometer- a device for measuring electrical current. Also called an ampmeter. • Electric motor- a device that uses a electromagnet in the field of a permanent magnet to produce rotational motion. • A (DC) electric motor requires a commutator to interrupt and change the direction of the electric current Definition 3 • Electric generator – a device that changes the motion of a coil rotating in the field of a permanent magnet to produce an electric current. • The current produced by a generator changes direction twice in each revolution of the coil. The current produced by a generator is called Alternating Current. • With modifications a generator can produce direct current. Definition 4 • Transformer- a device that changes the voltage of electric current. • Primary coil – the coil through which the input current flows. • Secondary coil – the coil through which the output current is produced. • Core – the iron around which both the input coil and the output coil are wound. Example (Page 244) Assignment- Applying Math 6 If the input voltage is 120 volts and the primary coil (input) has 100 turns, what will the output voltage be if there are 10 turns on the secondary (output) coil? V input # input coils 120V 100 = V output # output coils = V output 10