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© Boardworks Ltd 2003 Electromagnets Core Describe the pattern of the magnetic field due to currents in straight wires and in solenoids Describe applications.

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Presentation on theme: "© Boardworks Ltd 2003 Electromagnets Core Describe the pattern of the magnetic field due to currents in straight wires and in solenoids Describe applications."— Presentation transcript:

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2 © Boardworks Ltd 2003 Electromagnets Core 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 relay Supplement 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.

3 © Boardworks Ltd 2003 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 materials Non-magnetic materials

4 © Boardworks Ltd 2003 Magnets and materials N S What materials are magnets made from? Iron or steel. What materials will magnets stick to? Iron or steel. And nickel!

5 © Boardworks Ltd 2003 Repulsion and attraction Repel/attract Unlike poles attract. Like poles repel.

6 © Boardworks Ltd 2003 Revising magnetism I Magnets are made from which materials? ___________ What are the ends of a magnet called? __________ What do we call the area around a magnet where a magnetic force exists? __________________ What does the word attract mean?__________ What does the word repel mean?__________ Iron or steel The Poles The Magnetic Field Pull together Push apart

7 © Boardworks Ltd 2003 What will two north poles do if brought together? _____ What will two south poles do if brought together? ______ What will a north and a south pole do if brought together? _______ What materials are attracted by magnets? ___________ Is magnetism a contact or non-contact force? _________ Repel Attract Iron and steel Non-contact Revising magnetism II

8 Magnetic field around a straight wire Use the right hand grip rule to find the field direction

9 Magnetic field around a solenoid Two rules to find the poles Grip rule no. 2 N and S rule

10 © Boardworks Ltd 2003 Making an electromagnet: Apparatus: Batteries Wire Iron Nail What to do: 1.Wrap a coil of wire around the iron nail. 2.Connect the coil of wire to the batteries. 3.See how strong the magnet is.

11 © Boardworks Ltd 2003 Results How many paperclips could you pick up? Can you think of any ways to make the electromagnet stronger? More batteries (more current) Number of paperclips Number of batteries More turns of wire on the coil Number of paperclips Number of turns

12 © Boardworks Ltd 2003 Ways to make an electromagnet stronger There are three ways to make an electromagnet stronger. Do you know them? 1.___________________ 2.___________________ 3.___________________ More turns on the coil More electrical current Using an iron core S N What happens if you turn the battery around in an electromagnet? S The poles on the coil reverse, north becomes south and south becomes north.

13 relays http://www.explainthatstuff.com/howrelaysw ork.html http://www.explainthatstuff.com/howrelaysw ork.html A relay uses a small current to turn on a larger current Eg a car starter motor

14 Relay diagram

15 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

16 © Boardworks Ltd 2003 What do like poles do? A.Attract and repel B.Attract C.Repel D.Stick together

17 © Boardworks Ltd 2003 Which material below will not stick to a magnet? A.Steel paper clip B.Aluminium can C.Iron nail D.Steel key

18 © Boardworks Ltd 2003 Which of the below will not increase the strength of an electromagnet? A.More coils B.More current C.Less current D.Iron core

19 © Boardworks Ltd 2003 In which direction do magnetic field lines always point? A.East to west B.West to east C.South to north D.North to south

20 © Boardworks Ltd 2003 Which of the following is not a use of electromagnets? A.Fridge magnets B.Loud speakers C.Relays D.Circuit breakers

21 © Boardworks Ltd 2003 Plenary: Magnetic Effect of Current Study the diagram of an electric bell, then put the statements into the correct order Current flows through electromagnet Magnetic field produced Magnetic field attracts armature Armature moves towards electromagnet Hammer strikes gong, circuit is broken Armature no longer attracted to coil Armature springs back Circuit is complete again


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