Presentation on theme: "Chapter 21 – Prentice Hall Physical Science"— Presentation transcript:
1 Chapter 21 – Prentice Hall Physical Science MagnetismChapter 21 – Prentice Hall Physical Science
2 Magnetic Force Magnetic Force: the force a magnet exerts on either another magneton iron (or similar metal)on moving chargesMagnetic poles: regions in a magnet where the magnetic force is strongestAll magnets have two poles: north and south.Like poles repel; Unlike poles attract.
3 Magnetic FieldsMagnetic field: the direction and strength of magnetic forces in a region around a magnetStrongest around the poles of a magnetField lines point FROM the north pole TO the south poleMagnetosphere: Area surrounding Earth affected by Earth’s magnetic fieldBill Allan, Katja Riedel, Richard McKenzie, Sylvia Nichol and Tom Clarkson. 'Atmosphere', Te Ara - the Encyclopedia of New Zealand, updated 21-Sep-2007 URL:Iron filings and compasses show the shape and direction of the magnetic field. (Source:
4 Magnetic Field lines around a magnet. The field comes out of the North end of the magnet and goes into the South end of the magnet. The field is strongest at the poles. Notice the lines are closer together there.
5 Magnetic DomainsA region in which many atoms have their magnetic fields aligned is called a magnetic domain
7 Magnetic MaterialsFerromagnetic: material that can be magnetized because it contains magnetic domainsIn an unmagnetized material, the magnetic domains are randomly aligned.In a magnetized material, the domains have been aligned by placing the material in a magnetic field.Source:
10 Electricity and Magnetism Electromagnetic force: force associated with charged particlesElectric force results from charged particles.Magnetic force results from moving charges.+Velocity of moving charge(coming out of the page/screen toward you)Force of magnetic field on the chargeNS
11 Solenoids and Electromagnets Solenoid: a coil of current carrying wireThe inside of a solenoid coil is like a bar magnet.If you place iron or nickel in the center of the coil, it will become magnetized. This is called an electromagnet.Electromagnet strength depends on:# of coilsCurrent (controlled by voltage and resistance of wires in circuit)
12 What is an electromagnet? When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.
13 Strength of electromagnet As the motion of the electrons around the wire (current) increases, the strength of the magnetic field increasesAs the number of coils increase, the electromagnet strength increases
19 Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction.A generator is used to convert mechanical energy into electrical energy by electromagnetic induction.
22 Electrical Generation Electric generators are used to produce AC current.Mechanical energy moves the turbine containing the magnet, which in turns moves electrons to produce electricity.The turbine can be moved by:Nuclear reactions that heat water to create steam.Burning fossil fuels to heat water to create steam.Moving water to move the turbine.Wind blowing to move the turbineGeothermal resources to move the turbineRenewable vs. non-renewable methods.Geothermal heating & coolingSolar electricity for your home - RSG
23 Electromagnetic Devices Generators: convert mechanical energy into electrical using an electromagnetSee PhET SimulatonElectric Motors: use electrical energy through electromagnet to create mechanical energy (i.e. to turn an axle)
24 AC GeneratorsProduce alternating current: charge flows first in one direction, then in anotherUsed by most power plants todayA loop of wire spinning through a magnetic field will create an alternating current. Note: current will flow only if the circuit connected to the generator is complete.Source:
25 DC GeneratorsProduce direct current: charge flows in only one direction out of the generatorUsed in smaller applicationsElectric current in the loop of a DC generator alternates—that is, it changes directions—but in the outer circuit it travels in only one direction, and drops to zero twice with each rotation of the loop. By arranging more loops, a steadier direct current can be obtained.Source: "direct-current motor: electric current alternation." Online . Britannica Student Encyclopædia. 24 Mar. 2009 <
26 TransformersTransformer: device that increases or decreases the voltage and current of two linked AC circuitsUsed because electrical energy transmitted over large distances must travel at high voltages in order to reduce energy lossesChanges voltage and current with 2 solenoids (or coils) that have different numbers of turnsSource:
27 Step-down Transformer Types of TransformersNamed by what the transformer does to the voltageStep-up transformer:INCREASES voltageDecreases currentStep-down transformer:DECREASES voltageIncreases current240,000 VStep-up Transformer11,000 VVStep-down Transformer