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Summary Sheets 8J Magnets and electromagnets 8 J Magnetism is a non-contact force. Magnets attract magnetic materials. Iron, nickel and cobalt are magnetic materials. Mixtures, like steel, that include a magnetic material will also be attracted to a magnet. Other metals, like aluminium, are not magnetic and will not be attracted to a magnet. Iron oxide is a compound that is a magnetic material. It is used to make video and music cassettes and computer discs. Magnetic materials can also block magnetism. You can make a magnet from a piece of iron or steel. Always stroke in the same direction. magnet magnetic material ● ● ● ● The two ends of a bar magnet are called the north seeking pole and the south seeking pole or north pole and south pole for short. A north pole and a south pole attract each other. Two north poles or two south poles will repel each other. The space around a magnet where it has an effect is called its magnetic field. S N This is the shape of the magnetic field of a bar magnet. You can find the shape of the magnetic field using iron filings or using a plotting compass. The Earth has a magnetic field. A compass is a small magnet that always points north. But magnetic materials placed near a compass can change the direction that it points. Magnets can be used to sort iron and aluminium cans for recycling. Only the iron cans are attracted to the magnet. Magnets can also be used for holding fridge doors shut, and in compasses that sailors or walkers use. A wire with electricity flowing through it has a magnetic field around it. An electromagnet is a coil of wire with an electric current flowing through it. Page 1 of 2 Exploring Science for QCA Copymaster File 8 454 © Pearson Education Limited 2002 8J Summary Sheets (continued) You can make an electromagnet stronger by: ● ● ● increasing the number of coils of wire increasing the size of the current (by increasing the voltage) using an iron core. 8 J Electromagnets can be used for lifting things. They are also used in electric bells, relays and in video and music recording. Electromagnets are used to make bells work. cell pivot springy metal electromagnet contact gong armature A reed switch has two thin pieces of iron inside it. If a magnet is held near the switch, the pieces of iron are magnetised and touch each other. A reed switch can also be switched on using an electromagnet. Any switch that is worked by electricity is called a relay. Relays are used to make things safer. For example, the starter motor in a car uses a high current and needs thick wires for the current to flow through. A relay is used in a car so that the driver does not have to touch any part of the circuit that has a high current. circuit 1 When current flows in circuit 1 the coil becomes an electromagnet. contacts iron armature circuit 2 coil of wire When the armature moves the iron connects the two contacts and electricity can flow in circuit 2. The iron armature is attracted by the electromagnet. Page 2 of 2 Exploring Science for QCA Copymaster File 8 455 © Pearson Education Limited 2002 Target Sheet 8J Name 8 J Topic 8Ja 8Jb 8Jc 8Jd 8Je Class 1 Target Know which materials are magnetic. 2 Know some properties of magnetic materials. 3 Know which materials will block magnetism. 4 Know the rules for magnets attracting and repelling. 1 Know the names of the two ends of a magnet. 2 Know which way a compass needle points. 3 Know what magnetic compasses are used for. 4 Know how to make a magnetic compass. 1 Know what a magnetic field is. 2 Know the shape of a magnetic field around a bar magnet. 3 Know the direction of a magnetic field. 4 Know about the Earth’s magnetic field. 1 Know what an electromagnet is. 2 Know how to make an electromagnet stronger. 3 Know how an electric bell works. 4 Know why relays are used in car starter motor circuits. 1 Know what causes a magnetic field around a wire. 2 Know the shape of the magnetic field around an electromagnet. 3 Know why a core can make an electromagnet stronger. 4 Know the shape of the magnetic field around a straight wire. Exploring Science for QCA Copymaster File 8 Before the unit 448 I have learned this I have revised this © Pearson Education Limited 2002 Word Sheets 8J Word sheets that include new words from the ‘Focus on:’ pages are available on the Exploring Science website. 8 J 8Ja – Magnetic attraction Word attract Pronunciation Meaning Two things pulling towards each other. cobalt cO-balt A metal that is a magnetic material. iron A metal that is a magnetic material. magnet Something that can attract magnetic materials. magnetic materials Materials that are attracted to a magnet; iron, cobalt, nickel and steel are all magnetic materials. magnetism A non-contact force. nickel A metal that is a magnetic material. north pole One end of a magnet. This ends points north if the magnet can move. repel Push away. south pole One end of a magnet. steel A mixture made mainly from iron; it is a magnetic material. 8Jb – Pointing north Word bar magnet Pronunciation Meaning A straight magnet, shaped like a small bar. compass A magnetised piece of metal that can swing around – it points north. north-seeking pole The end of a magnet that points north if the magnet can move freely. Often just called the north pole. south-seeking pole The end of a magnet that points south if the magnet can move freely. Often just called the south pole. 8Jc – Force field Word iron filings Pronunciation f-eye-lings Meaning Tiny pieces of iron that are sometimes used to find the shape of a magnetic field. magnetic field The space around a magnet where it can affect magnetic materials or other magnets. north magnetic pole The place on the Earth where compasses point (it is not in the same place as the North Pole marked on maps). plotting compass A small compass used for finding the direction of a magnetic field. Page 1 of 2 Exploring Science for QCA Copymaster File 8 449 © Pearson Education Limited 2002 8J Word Sheets (continued) 8Jd – Sounds magnetic/Keep your distance 8 J Word armature Pronunciation Meaning The iron part of a relay that moves when electricity is flowing in the solenoid (or electromagnet). electromagnet A coil of wire with electricity flowing in it. An electromagnet has a magnetic field like a bar magnet. make and break switch The switch in an electric bell that opens and closes. It is operated by an electromagnet that breaks the circuit whenever it is switched on. permanent magnet A magnet that keeps its magnetism – it does not depend on electricity. reed switch A switch made from two thin pieces of metal, which closes when it is in a magnetic field. relay A switch that is switched on and off by electricity. solenoid A coil of wire. 8Je – Coils and cores Word core Pronunciation Meaning A solid bar inside an electromagnet – usually made of iron. Page 2 of 2 Exploring Science for QCA Copymaster File 8 450 © Pearson Education Limited 2002 Summary Sheets 8J Forces Balanced forces are forces that are the same size but work in opposite directions. If forces are balanced: 8 J • a stationary object stays stationary; • a moving object continues to move at the same speed. A car or motorbike uses the energy stored in fuel to move at a steady speed because it needs a force from the engine to balance the forces of air resistance and friction. The amount of air resistance on something can be reduced by giving it a smooth, streamlined shape. The air resistance increases as the speed increases, so cars use up more fuel per mile when they are travelling fast. Air resistance is caused by air particles hitting the moving object. The particles transfer energy to the object, which is why objects moving through air can get hot. Pressure on solids Pressure is the amount of force pushing on a certain area. For a certain area, the bigger the force, the bigger the pressure. For a certain force, the bigger the area, the smaller the pressure. In this picture, the thumb is putting a force onto the head of the pin. The force is transferred to the point of the pin. The point has a very small area, so there is a very large pressure on the board, and the pin goes in. In this picture, the thumb is putting a force directly on the board. The area of the thumb is much larger than the area of the pin point, so there is only a small pressure on the board. The thumb does not go into the board. Sharp knife – a small area giving a large pressure. Snow shoes – a large area giving a small pressure. Magnets and electromagnets Magnetism is a non-contact force. A magnet does not have to be touching something to attract it. Magnets attract magnetic materials. Iron, nickel and cobalt are magnetic materials. Mixtures, like steel, that include a magnetic material will also be attracted to a magnet. Other metals, such as aluminium or copper, are not magnetic and will not be attracted to a magnet. • The two ends of a bar magnet are called the north-seeking pole and the south-seeking pole, or north pole and south pole for short. • A north pole and a south pole attract each other. Exploring Science M010_ES_AB_Y8_5415_U8J.indd 284 edition 284 Page 1 of 2 © Pearson Education Limited 2008 28/8/08 13:20:18 8J Summary Sheets (continued) • Two north poles or two south poles repel each other. A bar magnet is a permanent magnet, because it is always magnetic. A wire with electricity flowing through it has a magnetic field around it. An electromagnet is a coil of wire with an electric current flowing through it. It is only magnetic while the current is flowing. 8 J You can make an electromagnet stronger by: • increasing the number of coils of wire • increasing the size of the current (by increasing the voltage) • using an iron core. Magnetic fields The space around a magnet where it has an effect is called its magnetic field. S You can find the shape of the magnetic field using iron filings or using a plotting compass. The Earth has a magnetic field. A compass is a small magnet that will point towards the Earth’s North pole. But magnetic materials placed near a compass can change the direction that the compass points towards. N This is the shape of the magnetic field of a bar magnet. The magnetic field of an electro magnet is a similar shape. Levers Forces can be used to turn objects around pivots. A pivot is also known as a fulcrum. Levers work by magnifying the force that is put in (the effort) or they can make the load move further than the effort. The amount the force or distance is multiplied depends on the distances between the load and the pivot and the effort and the pivot. The hammer is acting as a force multiplier. force from hand biceps muscle effort triceps muscle radius bone pivot The arm is acting as a distance multiplier. Exploring Science M010_ES_AB_Y8_5415_U8J.indd 285 edition 285 Page 2 of 2 © Pearson Education Limited 2008 28/8/08 13:20:19 Level Ladder 8J Name Class My Target Level is: 8 J Date My final level is: Tick the boxes that apply. Or use traffic lights to show how confident you are (red = ‘I don’t know this’; orange = ‘I’m not very confident about this’; green = ‘I’m confident I know this’). Level At the end of the Unit: I can do this This needs more work Working towards Level 4 Follow instructions and work safely during practical work. Describe how magnets can affect magnets and other materials. Level 4 Recall what a magnetic field is, and that the Earth has one. Describe how the features of different types of transport make them suited for their purposes. Appreciate some of the reasons why we depend on transport. Use iron filings to show the shape of a magnetic field. Present data from investigations as bar charts. Recall that electromagnets need electricity to stay magnetised. Level 5 Explain how pressure can be changed in a variety of circumstances. Describe some technological developments that have lead to today’s forms of transport. Estimate quantities to use in calculations. Use a compass to plot the shape of a magnetic field. Recall what drag is and the factors that affect it. Recall how pressure depends on force and area, and some ways in which pressure can be reduced or increased. Describe how levers can be used. Describe the shapes and directions of the magnetic fields of bar magnets, electromagnets and combinations of magnets. Explain why compasses work. Explain how simple levers work, and some of their uses. Page 1 of 2 Exploring Science M010_ES_AB_Y8_5415_U8J.indd 282 edition 282 © Pearson Education Limited 2008 28/8/08 13:20:16 Level Ladder (continued) 8J Level At the end of the Unit: I can do this This needs more work Level 6 Use the idea of particles to explain air resistance. 8 J Explain why a vehicle needs a force from the engine to keep moving at a constant speed, and the effects of this on fuel consumption and the need for streamlining. Level 7 Link conclusions to scientific understanding. Use graphs of my results to decide if two variables are proportional or inversely proportional. Evaluate the reliablity of evidence. Describe the different classes of levers and how they can be used. Level 8 Use ideas about the Earth’s magnetic field to explain the meanings of variation, dip and deviation. Use ideas about domains to explain how to create and destroy magnets. Recall that the shape of the field around a current-carrying wire is circular. Recall the meaning of coefficient of drag and use it in calculations. Page 2 of 2 Exploring Science M010_ES_AB_Y8_5415_U8J.indd 283 edition 283 © Pearson Education Limited 2008 28/8/08 13:20:16 Word Sheets 8J 8Ja – Drag act Word Pronunciation Meaning air resistance A force that tries to slow things down that are moving through the air. It is a type of friction, and is also called drag. balanced forces Two forces that are the same strength and working in opposite directions. drag Air resistance and water resistance are both also called drag. streamlined Something that has a smooth shape to reduce the air resistance or water resistance. water resistance A force that tries to slow things down that are moving through water. It is a type of friction, and is also called drag. 8 J 8Jb – Tracks and trains Word Pronunciation Meaning pascal A unit for pressure. 1 Pa = 1 N/m2 pressure A way of saying how spread out a force is. 8Jc – Floating trains Word Pronunciation Meaning attract Pull towards. bar magnet A straight magnet shaped like a small bar. cobalt cO-balt A metal that is a magnetic material. core A solid bar inside an electromagnet, usually made of iron. electromagnet A coil of wire with electricity flowing in it. iron A metal that is a magnetic material. maglev Trains that use electromagnets to make them float (or levitate), above the tracks and move along are called maglev trains. magnet Something that can attract magnetic materials. magnetic material Material that is attracted to a magnet; iron, cobalt, nickel and steel are all magnetic materials. magnetism A non-contact force. nickel A metal that is a magnetic material. non-contact force A force, such as magnetism or gravity, that does not need to be touching something to have an effect. north pole One end of a magnet. This end points north if the magnet is free to move. permanent magnet A magnet that keeps its magnetism – it does not depend on electricity. repel Push away. Page 1 of 2 Exploring Science M010_ES_AB_Y8_5415_U8J.indd 275 edition 275 © Pearson Education Limited 2008 28/8/08 13:20:10 Word Sheets (continued) 8J 8Jc – Floating trains (continued) Word 8 J Pronunciation Meaning south pole One end of a magnet. This end points south if the magnet is free to move. steel A mixture made mainly from iron; it is a magnetic material. 8Jd – Finding the way Word Pronunciation Meaning compass A magnetised piece of metal that can swing around – it points north. magnetic field The space around a magnet where it can affect magnetic materials or other magnets. north-seeking pole The end of a magnet that points north if the magnet can move freely. Often just called the north pole. plotting compass A small compass used for finding the direction of a magnetic field. south-seeking pole The end of a magnet that points south if the magnet can move freely. Often just called the south pole. 8Je – Change your attitude/What next for transport? Word Pronunciation Meaning ailerons Flaps on the ends of an aeroplane’s wing, that help to control it. biceps muscle The muscle on the front of the upper arm that makes the arm bend. distance multiplier A lever where the load moves further than the effort. effort The force put on something, especially a lever. force multiplier A lever where the load is bigger than the effort. fulcrum A point about which something turns. Another name for a pivot. lever A simple machine that can increase the size of a force, or increase the distance the force moves. load The weight or force on something. pivot A point about which something turns. Another name for a fulcrum. radius bone The bone between the elbow and wrist that the biceps muscle pulls on. sustainable A way of living that does not use up non-renewable resources or harm things in our surroundings. Something that is sustainable allows things to continue into the future. Page 2 of 2 Exploring Science M010_ES_AB_Y8_5415_U8J.indd 276 edition 276 © Pearson Education Limited 2008 28/8/08 13:20:10