EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1Magnetism and ElectromagnetismEdexcel IGCSE Physics pages 179 to 186September 19th 2012Content applying to Triple Science only is shown in red type on the next slide and is indicated on subsequent slides by TRIPLE ONLY
Edexcel SpecificationSection 6: Magnetism and electromagnetism b) Magnetismunderstand that magnets repel and attract other magnets and attract magnetic substancesdescribe the properties of magnetically hard and soft materialsunderstand the term magnetic field lineunderstand that magnetism is induced in some materials when they are placed in a magnetic fielddescribe experiments to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnetsdescribe how to use two permanent magnets to produce a uniform magnetic field pattern.c) Electromagnetismunderstand that an electric current in a conductor produces a magnetic field round itdescribe the construction of electromagnetssketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a currentRed type: Triple Science Only
Magnets and magnetic materialsMagnets attract objects made of magnetic materials
Magnetic materials include the elements iron, nickel, cobalt, alloys containing some of these such as steel and some of their compounds.TRIPLE ONLY
Hard and soft magnetic materialsPermanent magnets are made of magnetically HARD materials such as steel. These materials retain their magnetisation once magnetised.Magnetically SOFT materials, such as iron, lose their magnetisation easily. They suitable for temporary magnets such as electromagnets.TRIPLE ONLY
Magnetic polesMagnetic poles are the parts of a magnet that exert the greatest force.
Magnetic poles occur in pairs usually called north (N) and south (S)TRIPLE ONLY
Why poles are called north and southA magnet suspended so that it can rotate freely horizontally will eventually settle down with one pole facing north and the other south.
This is pole is therefore called the north seeking pole, usually shortened to just north pole.
The magnet has been orientated by the Earths magnetic field.
A compass is an application of this effect.TRIPLE ONLY
The law of magnetsLike poles repel unlike poles attract
Magnetic fieldsA magnetic field is a volume of space where magnetic force is exerted.
All magnets are surrounded by magnetic fields.
The shape of a magnetic field can be shown by iron filings or plotting compasses.
Magnetic field around a bar magnet
Magnetic fields between two bar magnets
Producing a uniform magnetic fieldA uniform magnetic field exerts a constant force over a region.
Such a field will consist of parallel equally spaced magnetic field lines.
This type of field can almost be found between a north and south magnetic pole.
The Earths magnetic fieldThe earths magnetic field is similar in shape to that around a bar magnet.
It is thought to be caused by electric currents flowing through the molten outer core of the Earth.
At the present the field pattern is like that with a magnetic SOUTH pole situated somewhere below northern Greenland
Induced magnetismMagnetism can be induced in a magnetic material if it is placed within a magnetic field.
If the material is magnetically hard it will retain its magnetism once removed from the field.
Certain rocks in the Earths crust such as lodestone have been magnetised in this way by the Earths magnetic field.TRIPLE ONLYiron bar
Choose appropriate words to fill in the gaps below:Magnetic materials are either hard or ______. Hard magnetic materials such as ______ retain their magnetisation once magnetised. A magnetic _____ is a region where the magnetic force is greatest. Magnetic poles always occur in ______. Like poles _______, unlike attract.A magnetic ______ is a region where magnetic force is exerted. The ________ of the magnetic field around a bar magnet is from north to south.softrepelfieldsteeldirectionpolepairsWORD SELECTION:TRIPLE ONLYsoftrepelfieldsteeldirectionpolepairs
ElectromagnetismIn 1820 Hans rsted noticed that a wire carrying an electric current caused a compass needle to deflect.
Magnetic field patterns around wires1. Straight wireTRIPLE ONLYThe magnetic field consists of concentric circles centred on the wire.The magnetic field is strongest near the wire. This is shown by the field lines being closest together near to the wire.The strength of the field increases if the electric current is increased.
The right-hand grip rule (for fields)TRIPLE ONLYGrip the wire with the RIGHT hand.The thumb is placed in the direction of the electric current.The fingers show the direction of the circular magnetic field.
Complete the diagrams below:TRIPLE ONLYElectric current out of the pageElectric current into the pageAdd field arrowsAdd field arrowsAdd current directionAdd current direction
2. Flat circular coilTRIPLE ONLY
3. SolenoidA solenoid is a coil of wire carrying an electric current.
The magnetic field is similar in shape to that around a bar magnet.
The strength of the field increases with: the electric current the number of turns in the coil
The right-hand grip rule (for poles)TRIPLE ONLYGrip the coil with the RIGHT hand.The fingers are placed in the direction that the eclectic current flows around the coil. The thumb points towards the north pole end of the coil.
Complete the diagrams below:TRIPLE ONLY1. Locate north4. Add coils3. Add current direction2. Locate southNSN
ElectromagnetsAn electromagnet consists of a current carrying coil wrapped around an iron core.TRIPLE ONLY
Uses of electromagnets1. Scrap yard crane
The iron core of the electromagnet is a SOFT magnetic material.
When current flows the iron becomes strongly magnetised and so picks up the scrap iron and steel.
When the current is turned off the iron loses its magnetisation and so releases the scrap.
2. The electric bellWhen the push switch is closed current flows around the circuit turning on the electromagnet.
The soft iron armature is pulled towards the electromagnet and the hammer hits the gong.
This causes the contact switch to open cutting off the electric current.
The spring now pulls the armature back again closing the contact switch.
Current now flows again and the hammer hits the gong again.
TRIPLE ONLYgonghammerelectromagnetpush switchspringcontact switchsoft iron armature
Label the diagram of the electric bell below:TRIPLE ONLYContact switch
3. The relay switchA relay switch is a way of using a low voltage circuit to switch remotely a high voltage (and possibly dangerous) circuit.
When switch A is closed, the small current provided by the cell causes the electromagnet to become magnetised..
The iron armature is then attracted to the electromagnet causing the springy contact switch B to close in the high voltage circuit.TRIPLE ONLYswitch Aspringy contact switch Biron armaturehingeelectromagnetto high voltage circuit
4. Circuit breakerCurrent normally flows between terminals A and B through the contact and the electromagnet.
When the current in a circuit increases, the strength of the electromagnet will also increase. This will pull the soft iron armature towards the electromagnet.
As a result, spring 1 pulls apart the contact and disconnecting the circuit immediately, and stopping current flow.The reset button can be pushed to bring the contact back to its original position to reconnect the circuit
Choose appropriate words to fill in the gaps below:A wire carrying an electric ______ produces a magnetic field. This field increases in ________ if the current is increased.A ________ is a coil of wire carrying an electric current. The field produced increases in strength if the number of _____ in the coil is increased or if _____ is placed inside the coil.An ____________ consists of a coil of a solenoid wrapped around an iron core. Iron is a ______ magnetic material that loses its magnetisation once the current in the coil is switched off.solenoidstrengthironsoftturnscurrentelectromagnetWORD SELECTION:TRIPLE ONLYsolenoidstrengthironsoftturnscurrentelectromagnet
Online SimulationsBar magnet field - Fendt Faraday Electromagnetic Lab - PhET - Play with a bar magnet and coils to learn about Faraday's law. Move a bar magnet near one or two coils to make a light bulb glow. View the magnetic field lines. A meter shows the direction and magnitude of the current. View the magnetic field lines or use a meter to show the direction and magnitude of the current. You can also play with electromagnets, generators and transformers! Field around a straight conductor - Fendt Magnetic field around a straight wire / coil / solenoid - NTNURelay demonstration - Freezeway.com Electric Bell demonstration - Freezeway.comBBC KS3 Bitesize Revision: Bar Magnets Magnetic Fields Electromagnets Using Electromagnets - includes an applet showing how an electric bell works
Magnetism and Electromagnetism Notes questions from pages 179 to 186State what happens when different types of magnetic poles are placed near to each other. (see page 180)(a) What is the difference between magnetically soft and hard materials? (b) Give examples and uses of each type. (see page 180)(a) Draw the magnetic field patterns between and around magnets shown on page 181.(b) Explain what the magnetic