Presentation on theme: "Electromagnets Core • Describe the pattern of the magnetic field due to currents in straight wires and in solenoids • Describe applications of the magnetic."— Presentation transcript:
1 ElectromagnetsCore• Describe the pattern of the magnetic field due to currents in straight wires and in solenoids• Describe applications of the magnetic effect of current, including the action of a relaySupplement• State the qualitative variation of the strength of the magnetic field over salient parts of the pattern• Describe the effect on the magnetic field of changing the magnitude and direction of the current.
2 What materials will stick to magnets? Look around the laboratory or your teacher will provide a tray.See which materials will stick to a magnet and which materials will not.Magnetic materialsNon-magnetic materials
3 What materials will magnets stick to? Magnets and materialsWhat materials are magnets made from?Iron or steel.NSWhat materials will magnets stick to?Iron or steel.And nickel!
4 Repulsion and attraction Repel/attractRepel/attractRepel/attractUnlike poles attract.Like poles repel.
5 Revising magnetism I Iron or steel Magnets are made from which materials? ___________The PolesWhat are the ends of a magnet called? __________What do we call the area around a magnet where amagnetic force exists? __________________The Magnetic FieldPull togetherWhat does the word attract mean? __________What does the word repel mean? __________Push apart
6 Revising magnetism II Repel What will two north poles do if brought together? _____RepelWhat will two south poles do if brought together? ______RepelWhat will a north and a south pole do if broughttogether? _______AttractIron and steelWhat materials are attracted by magnets? ___________Is magnetism a contact or non-contact force? _________Non-contact
7 Magnetic field around a straight wire Use the right hand grip rule to find the field direction
8 Magnetic field around a solenoid Two rules to find the polesGrip rule no. 2N and S rule
9 Making an electromagnet: Apparatus:BatteriesWireIron NailWhat to do:Wrap a coil of wire around the iron nail.Connect the coil of wire to the batteries.See how strong the magnet is.
10 Results How many paperclips could you pick up? Can you think of any ways to make the electromagnetstronger?More batteries (more current)Number of paperclipsNumber of batteriesMore turns of wire on the coilNumber of paperclipsNumber of turns
11 Ways to make an electromagnet stronger There are three ways to make an electromagnet stronger. Do you know them?___________________More turns on the coilMore electrical currentUsing an iron coreSSNWhat happens if you turn the battery around in an electromagnet?The poles on the coil reverse, north becomes south and south becomes north.
12 relays http://www.explainthatstuff.com/howrelayswork.html A relay uses a small current to turn on a larger currentEg a car starter motor
14 The power source for both circuits may be the same (the resistance determines the size of the current)There are several other arrangements that would have the same effect eg a plunger arrangement
15 Attract and repel Attract Repel Stick together What do like poles do?Attract and repelAttractRepelStick together
16 Which material below will not stick to a magnet? Steel paper clipAluminium canIron nailSteel key
17 Which of the below will not increase the strength of an electromagnet? More coilsMore currentLess currentIron core
18 In which direction do magnetic field lines always point? East to westWest to eastSouth to northNorth to south
19 Which of the following is not a use of electromagnets? Fridge magnetsLoud speakersRelaysCircuit breakers
20 Plenary: Magnetic Effect of Current Study the diagram of an electric bell, then put the statements into the correct orderMagnetic field producedCircuit is complete againMagnetic field attracts armatureHammer strikes gong, circuit is brokenArmature moves towards electromagnetArmature no longer attracted to coilArmature springs backCurrent flows through electromagnet