MAGNETISM 1

Magnetic Force 2  Magnetic Force: the force a magnet exerts on either  another magnet  on iron (or similar metal)  on moving charges  Magnetic poles: regions in a magnet where the magnetic force is strongest  All magnets have two poles: north and south.  Like poles repel; Unlike poles attract.

Magnetic Fields 3  Magnetic field: the direction and strength of magnetic forces in a region around a magnet  Strongest around the poles of a magnet  Field lines point FROM the north pole TO the south pole  Magnetosphere: Area surrounding Earth affected by Earth’s magnetic field Iron filings and compasses show the shape and direction of the magnetic field. (Source: champions.com/science/magnetic_detection.htm) champions.com/science/magnetic_detection.htm Bill Allan, Katja Riedel, Richard McKenzie, Sylvia Nichol and Tom Clarkson. 'Atmosphere', Te Ara - the Encyclopedia of New Zealand, updated 21-Sep-2007 URL:

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.

Magnetic Domains  A region in which many atoms have their magnetic fields aligned is called a magnetic domain

Magnetic domains and field lines

Magnetic Materials 7  Ferromagnetic: material that can be magnetized because it contains magnetic domains Source: In 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.

Attraction and Repulsion AttractionRepulsion

Attraction/Repulsion

Electricity and Magnetism 10  Electromagnetic force: force associated with charged particles  Electric 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 charge NSSN

Solenoids and Electromagnets 11  Solenoid: a coil of current carrying wire  The 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 coils  Current (controlled by voltage and resistance of wires in circuit)

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.

Strength of electromagnet  As the motion of the electrons around the wire (current) increases, the strength of the magnetic field increases  As the number of coils increase, the electromagnet strength increases  You can make an electromagnet stronger by (1) putting more turns of wire in the coil or (2) making a larger soft iron core, or (3) increasing the current through the wire.

What are electric motors? An electric motor is a device which changes electrical energy into mechanical energy.

Go to the next slide  How does an electric motor work?

Simple as that!!

 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.

Electric Generator PHET APPLET

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. Nuclear reactions  Burning fossil fuels to heat water to create steam. Burning fossil fuels  Moving water to move the turbine. Moving water  Wind blowing to move the turbine Wind  Geothermal resources to move the turbine Geothermal  Renewable vs. non-renewable methods.  Geothermal heating & cooling Geothermal  Solar electricity for your home - RSG Solar homeRSG

Electromagnetic Devices 21  Generators: convert mechanical energy into electrical using an electromagnet  See PhET SimulatonPhET Simulaton  Electric Motors: use electrical energy through electromagnet to create mechanical energy (i.e. to turn an axle)

AC Generators  Produce alternating current: charge flows first in one direction, then in another  Used by most power plants today 22 A 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: insideacgenerator.html

DC Generators  Produce direct current: charge flows in only one direction out of the generator  Used in smaller applications 23 Electric 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

Transformers  Transformer: device that increases or decreases the voltage and current of two linked AC circuits  Used because electrical energy transmitted over large distances must travel at high voltages in order to reduce energy losses  Changes voltage and current with 2 solenoids (or coils) that have different numbers of turns 24 Source:

Types of Transformers  Named by what the transformer does to the voltage  Step-up transformer:  INCREASES voltage  Decreases current  Step-down transformer:  DECREASES voltage  Increases current 25 Step-up Transformer Step-down Transformer 11,000 V 240,000 V V

Electromagnetism  A moving electric field creates a magnetic field that rotates around it  A moving magnetic field creates an electric field that rotates around it  The Right Hand Rule helps describe this

The Right Hand Rule  First define positive electric current as flowing from the positive (+) end of a battery, through an electric circuit, and back into the negative (-) end.  Next define a magnetic field as always pointing away from a North pole and towards a South pole.

The Right Hand Rule  Curl your fingers in the direction of the rotating field.  Extend your thumb. It now points in the direction of the other field.  If your fingers are curling along with a rotating electric field, your thumb will point in the direction of the magnetic field and vice versa.

The Right Hand Rule

The Electromagnet By the Right Hand Rule, a coil of wire with current flowing in it will create a magnetic field The strength of the magnetic field depends on The amount of current in a wire – More current means stronger magnetic field The number of turns in the coil – More turns means stronger magnetic field The material in the coil – Magnetic materials like iron and steel make the magnetic field stronger

The Electromagnet  A simple electromagnet can be made by coiling some wire around a steel nail, and connecting a battery to it.  As current rotates around the nail, a magnetic field is created with the North pole at the bottom and the South pole at the top

The Electromagnet  Electromagnets are found in many everyday objects such as  Motors and generators  Doorbells  Speakers  Hard drives  VHS and Audio cassette tapes  Telephones

The Electric Motor An electric motor is a device that converts electromagnetic energy into mechanical energy It works by using special electromagnets in the case of the motor that create North and South poles that are constantly spinning in a circle. These spinning poles pull along magnets that are on the rotor (the part that spins), causing it to rotate

The Electric Generator  An electric generator works in the opposite of a motor; it converts mechanical energy into electromagnetic energy  An outside force moves magnets in a circle past several coils of wire.  By the Right Hand Rule, electric currents are developed in the coils of wire.