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E XP ERIM E NT MANUAL Magnetic Science Franckh-Kosmos Verlags-GmbH & Co. KG, Pfizerstr. 5-7, 70184 Stuttgart, Germany | +49 (0) 711 2191-0 | www.kosmos.de Thames & Kosmos, 89 Ship St., Providence, RI, 02903, USA | 1-800-587-2872 | www.thamesandkosmos.com Thames & Kosmos UK LP, 20 Stone Street, Cranbrook, Kent, TN17 3HE, UK | 01580 713000 | www.thamesandkosmos.co.uk SAFETY INFORMATION Dear a re s P n t a dult ot h e r (and o r s) is v r sup e This experiment kit uses lots of interesting experiments to give your child a playful introduction to magnets and magnetism. Please stand by your child’s side during the experiments and offer your support and guidance. Before starting the experiments, read through the manual together and be sure to follow it when performing the experiments. Please be careful not to let any of the kit parts get into the hands of young children. Have fun with the experiments! Warning! Do not bring the magnets close to television sets, computers, computer diskettes, music cassettes, videotapes, or ATM or credit cards. The data stored in them could be damaged or lost! →For the experiments, you will need one 1.5-volt AA-type battery, which could not be included in the kit due to its limited shelf life. →Under no circumstances are more or different batteries to be used than what is specified here. →Do not use rechargeable batteries. → Non-rechargeable batteries are not to be recharged. They could explode! → Never bring batteries into contact with other metal objects, such as key rings or coins. → Avoid bending or distorting batteries. → Never throw batteries into flame or store them near heat sources. → Do not use electrical outlets for any experiments! Never insert wires or other metal pieces into outlets! The electrical voltage (110 volts) can kill you! → When experimenting, avoid connecting the battery terminals directly to each other — the battery could explode! → Avoid short-circuiting the battery or batteries. → After the experiments, always completely disconnect the electrical or electromagnetic circuit from the battery and store separately. → E xhausted batteries are to be disposed of properly at collection locations, not simply thrown into the trash. →Do not mix old and new batteries. →Do not mix alkaline, standard (carbonzinc), or rechargeable (nickel-cadmium) batteries. WARNING! Not suitable for children under 8 years. This product contains small magnets. Swallowed magnets can stick together across intestines causing serious injuries. Seek immediate medical attention if magnets are swallowed. WARNING! Not suitable for children under 3 years. Choking hazard — small parts. WARNING! This kit contains functional sharp edges or points. Do not injure yourself! WARNING! Only for use by children aged 8 years and older. Instructions for parents or other supervising adults are included and have to be observed. Keep packaging and instructions as they contain important information. 1 CONTENTS Magnets, Iron, and Poles Pages 3 to 19 Learn all about the properties of your magnets. etism Electromagn Pages 37 to 43 n Build your ow t. e n g electroma Compass Pages 20 to 25 her Columbus How Christop cross the a found his way s open sea Magnetic Force and Magnetic Fields Pages 26 to 36 How to make invisible magnetic fields visible a G mes ets with Magn 8 4 to 4 Pages 4 ✔ CHECK IT OUT You will find su pplemental information o n pages 18, 19 , 25, 35, 36, 42, a nd 43. 665050-02-270217 2 KIT CONTENTS What’s in your experiment kit: 10 5 11 7 2 9 8 1 3 4 6 Checklist: Find – Inspect – Check off ✔ No. Description 1 2 3 4 5 6 7 8 9 10 11 Ring magnets (4) with stand Block magnet Ball magnets (set of 3) Plastic chips (approx. 25) Horseshoe and bar magnet set Compass Iron powder in plastic box Iron rod Wire Polystyrene disk Multicolored cardboard strip Qty. Item No. 1 1 1 1 1 1 1 1 1 1 1 704 443 704 444 709 255 704 446 704 447 000 276 704 449 011 297 000 064 702 235 709 280 Before doing anything else, please check all the parts against the list to make sure that nothing is missing. If you are missing any parts, please contact Thames & Kosmos customer service. Additional things you will need: 1.5-volt AA battery, scissors, adhesive tape, glue stick, paper, cardboard, permanent marker, string , ruler, bowl, saucer, needle, spoon, water, stopwatch, thick paper, various magnetic and nonmagnetic objects from around the house Any materials not contained in the kit are marked in italic script in the “You will need” boxes. Magnets, Iron, and Poles | 3 Magnets, Iron and Poles Over 2,500 years ago, scientists in ancient Greece made an astonishing discovery: Chunks of certain rocks exert a mysterious power over things made of iron. Since these rock chunks were primarily found near the ancient town of Magnesia in Asia Minor, they were called magnets. Today, magnets play an important role in many everyday and technical devices. You may know about magnetic closures on kitchen cupboard doors, for example. But you’ll also find magnets in speakers, in bicycle dynamos, and in multiple locations in cars. Now it’s time to learn about the mysterious nature of magnets... 4 EXPERIMENT 1 Lots of magnets YOU WILL NEED → all of the parts inside this kit 1 HERE'S HOW 1.Take all the parts except the magnets out of the experiment kit box and place them on a table. 2. Now take the bar magnet and watch what happens when you touch the objects on the table with it. What do you notice? Do the same thing with the horseshoe magnet, the block magnet, and the ball magnet. → WHAT’S HA PPENIN G? es of There are various typ ment kit . eri exp r magnets in you effect on an ve ha All of them will the iron er, wd po n the box with iro the d an ps, chi bar, the pla stic compa ss. four items to So you can use these t is a check whether an objec you can’t magnet — even when se the tell by looking, becau a pla stic magnet is hidden inside covering. nd for the So how about the sta gnet or not? ma a it ring magnet? Is 2 Magnets, Iron, and Poles | 5 EXPERIMENT 2 Mutual attraction 1 YOU WILL NEED → all of the magnets HERE'S HOW 1. Place two ball magnets a slight distance apart on the table. What do you notice? 2. Try to pull the two ball magnets apart. 3.Repeat the experiment with all the other magnets. What do you notice? TIP Magnets influence and interfere with each other. So you should always place only those magnets on the table that you need at that moment. Keep the other ones at least one meter away, so they don’t interfere with the ones you’re using. 2 → WHAT’S HA PPENIN G? Most magnets are ha rd to keep in one place. The ball ma gnets, in particular, roll toward each other and stick together. Bu t the others seem to find each oth er attractive as well. They exert a my sterious pull on each other, an d you really need to use some force to pull them apart again. So magnets exert a mu tual attraction on each oth er. Some will even flip around in the process. 6 EXPERIMENT 3 It all depends on the distance YOU WILL NEED 1 → horseshoe magnet → block magnet → iron rod HERE'S HOW 1. Move the iron rod towards the horseshoe magnet and note how strongly they stick together. 2 2. Now pull the rod away, gradually increase the distance between magnet and rod, and note the strength of the magnetic force at different distances. 3. Repeat the experiment with the block magnet. What’s the difference? → WHAT’S HA PPENIN G? exert on each The force that magnets of how far apart tor other is largely a fac are, the stronger y the they are. The closer t you’ll feel. But as the magnetic force tha r apart , the force you move them far the r. quickly grows weake you will feel a With the block magnet, l: It is somewhat stronger force overal horseshoe more powerful than the magnet. 3 Magnets, Iron, and Poles | 7 EXPERIMENT 4 Scientific expedition at home YOU WILL NEED 1 → horseshoe magnet → various household items WARNING! Make a wide detour around the TV, the computer (especially diskettes and magnetic media), video and music cassettes, and credit and debit cards: The magnet would destroy the data stored on them! HERE'S HOW 1.Walk around your house or apartment with the magnet, holding it up to various objects to see if it attracts them. 2.The following things would be good to investigate as you make your rounds: porcelain, glass, cardboard, paper, plastic, coins, furniture, cutlery, nails, needles, cooking pots, and paper clips. → WHAT’S HA PPENIN 2 G? magnet only You will notice that the ts, while others attracts certain objec in it at all. There’s don’t seem interested t: Magnets only an explanation for tha raction on things exert their force of att t contain iron. that are made of or tha use the magnet That means that you can s any iron to test whether there’ t. contained in an objec 8 EXPERIMENT 5 Iron turns into magnet 1 YOU WILL NEED → block magnet → iron rod → plastic chips HERE'S HOW 2 1. L ay the iron rod flat against the side of the block magnet, with its end projecting out beyond the magnet’s edge. 2.Spread the plastic chips out on the table and pass the iron rod over them. What happens? 3. Now separate the iron rod from the block magnet. → WHAT’S HA PPENIN G? l attract At first, the iron rod wil ps. So the one or more of the chi ract the magnet doesn’t only att the rod iron rod — it also makes rod in turn magnetic, so that the around the attracts the iron rings pla stic chips. ay from the The chips will drop aw you’ve ce on , iron rod, however magnet. ck blo removed it from the gnet ma a like The rod only act s e. on to d when it’s connecte 3 Magnets, Iron, and Poles | 9 EXPERIMENT 6 A new magnet is born 1 YOU WILL NEED → block magnet → iron rod → compass → long sewing needle 2 HERE'S HOW 1. Place the needle against the compass. 2. Do the same with the iron rod. 3. Now stroke the iron rod 50 to 70 times across one of the large surfaces of the block magnet. Important! Always stroke in the same direction across the same surface of the magnet. 4. Now move the block magnet far away and move the iron rod close to the compass needle again. 5. Now, stroke the sewing needle across the block magnet as you did in step 3, and look what happens when you hold the needle close to the compass. Keep the magnetized needle in a safe place — you’ll need it again later. 5 3 4 → WHAT’S HA PPENIN G? nt” with the block Without the “treatme needle won’t react magnet, the compa ss n rod or the sewing much to either the iro sewing needle needle (if it does, the d contact with a must already have ha n rod, still nothing magnet). With the iro nt” with the happens after “treatme edle, on the other magnet. The sewing ne ains its magnetic hand, astonishingly ret needle reacts force — the compa ss due to the fact that strongly to it. That is de of steel. Steel sewing needles are ma aining magnetic ha s the property of rem h a magnet. after being stroked wit 10 EXPERIMENT 7 Penetrating force YOU WILL NEED → block magnet → iron rod → cardboard, paper, knife made of steel, plastic wrap, fabric, aluminum foil → ruler 1 HERE'S HOW 1. Place the iron rod on a smooth table surface and see how close you can bring the block magnet before the rod starts to roll toward it. Make a note of the distance between magnet and rod when that happens. 2. Now slide a piece of cardboard in front of the block magnet. Is there a difference now in the distance at which the rod starts to roll toward it? Test the other materials as well by sliding them in front of the block magnet. → WHAT’S HA PPENIN G? netrates The magnetic force pe s without almost all the material gth at all. losing much of its stren really Only the steel knife is it. That ha s effective at blocking t steel to do with the fact tha contains iron. 2 Magnets, Iron, and Poles | 11 EXPERIMENT 8 Finding the force YOU WILL NEED → horseshoe magnet → block magnet → bar magnet → iron rod 1 HERE'S HOW 1. Place the individual magnets far apart from one another on the table. 2. Take the iron rod and use it to probe all the parts of the horseshoe magnet. Where do you feel the strongest force of attraction? Now, probe the block magnet and bar magnet as well. What do you notice? 2 → WHAT’S HA PPENIN G? h of the You will notice that eac ations loc n tai cer s magnets ha n more iro the ts rac where it att shoe rse ho the th Wi powerfully. ds en the it’s , ets gn and bar ma with ile wh t, ges on str that are the the large the block magnet it’s of a rts pa all t surfaces. No werful. po ly rm ifo un magnet are 12 NORTH EXPERIMENT 9 Exploring the poles YOU WILL NEED 1 → all the magnets HERE'S HOW 1. You will see the letters “N” and S” at the two ends of the bar magnet. These ends are known as “poles.” 2 2. Now approach one end of the horseshoe magnet with one end of the bar magnet. Then test the other end of the horseshoe magnet. Which ends attract each other, and which repel each other? 3. Probe all sides of the block magnet with both ends of the bar magnet. What do you determine? 3 4. Do the same thing with the ball magnets. Place them on a smooth surface for your investigation. → WHAT’S HA PPENIN G? es you can feel It’s strange: Sometim attraction, the expected force of two magnets the es but at other tim get together to nt wa don’t seem to s them she pu ing at all — someth l even wil ets gn ma ll apart . The ba in sh, fla a as ick flip around, qu pole g tin rac att ir the order to turn ds, or en o tw The et. gn to the bar ma dif ferent poles, apparently have properties. 4 Magnets, Iron, and Poles | 13 EXPERIMENT 10 Hidden poles YOU WILL NEED 1 → ball magnets → bar magnet → 2 different-colored permanent markers 2 HERE'S HOW 1. Take two balls and let them roll freely on the table a slight distance apart. They will quickly click together. 2. Pull them apart again, and mark the touching point (the point of contact) of one ball with one color, and that of the other ball with the other color. 3. Let all of the balls click together in turn, and make your marks on them. Important! Whenever you have used one color to mark one ball, be sure to use the other color to mark the other ball. 3 4. Use the bar magnet to test the marked locations. What do you notice? 4 → WHAT’S HA PPENIN SOUTH G? truth — The markings reveal the too. No les po o the balls have tw tains a con ll ba h wonder, since eac stic pla its ide ins tiny bar magnet cover. 14 EXPERIMENT 11 Jumping magnets YOU WILL NEED → 2 ring magnets HERE'S HOW 1. Place one ring magnet on the table. 2. Push the second ring magnet onto the first one with their two repelling sides facing each other. You will notice that it’s not so easy to do without making the lower one scoot away. 3. When you finally manage to do it, quickly let go. 1 2 → WHAT’S HA PPENIN The magnet will really into the air. G? jump up 3 Magnets, Iron, and Poles | 15 EXPERIMENT 12 Hovering magnets YOU WILL NEED 1 → all the ring magnets → ring magnet stand HERE'S HOW 1. Stack the ring magnets one on top of one another on the stand. Be sure that all the repelling sides are facing each other, so all the magnets end up hovering in the air. 2. Push down on the top magnet a little. What do you observe? 2 3. Now carefully remove the top ring magnet. What happens now? → WHAT’S HA PPENIN G? g magnet Even the ver y first rin few a will hover freely air. All of centimeters up in the ing above ver ho them will end up by an up ld he if one another, as invisible hand. on the top When you push down l also shift ring, the lower ones wil ugh there’s down a little, even tho rsely, the no direct contact. Conve a little lower ones will rise up top ring when you remove the magnet. 3 16 EXPERIMENT 13 Magical forces explained YOU WILL NEED 1 → all the ring magnets → iron rod HERE'S HOW 1. Stack the four ring magnets with their attracting poles facing one another. 2. Carefully insert the iron rod through the hole in the center. 2 3. Holding the “ring tower” together tightly, tip it so that you’d think the iron rod would fall. Does it fall? 3 → WHAT’S HA PPENIN G? ert the iron When you start to ins will feel a rod into the hole, you t, but then little resistance at firs get pulled ly the rod will practical so tightly it ld inside. The rings ho t won’t igh that even its own we a s re’ pull it out again. The inside ce for powerful magnetic in rod the the rings that holds place. Magnets, Iron, and Poles | 17 EXPERIMENT 14 Disappearing poles YOU WILL NEED 1 → bar magnet → horseshoe magnet → iron rod HERE'S HOW 1. Let your bar magnet stick to one end of the horseshoe magnet. 2. Now use the iron rod to test the magnetic force, particularly at the place where the poles meet. 2 3. Pull the magnets apart again. Now test all four ends with the iron rod. → WHAT’S HA PPENIN G? and the The horseshoe magnet single e bar magnet became on stuck re magnet when they we hardly together. That’s why you ce at for c detected any magneti But the t. me the place where they re. the ll sti two outer poles were pulled After the magnets are usly vio pre the apart again, ir the ain reg les attached po . gth former stren 3 18 MAGNETS POLES The magnets that people discovered thousands of years ago in nature were made of the mineral magnetite. This mineral, which forms grayish-brown crystals, is composed of iron and oxygen in a very specific ratio. Magnetite is created naturally through volcanic activity. Today, magnets can be produced artificially from compounds of the metals iron, nickel, and aluminum. But there are also some magnets that contain no iron at all. A lot of materials and material mixtures have been tested for their magnetic properties, and mixtures of relatively rare metals have been discovered that can make much stronger magnets than those found in nature. Those magnets don’t just attract iron, but will also attract the rarer metals nickel and cobalt almost as strongly. PERMANENT MAGNETS possess a magnetic force all on their own, and they retain it permanently. This experiment kit has numerous permanent magnets in different shapes, some with plastic coverings. These, too, are produced artificially, so they are stronger than natural magnetic rocks. The locations where a →→→→→→ ←←←←←← PERMANENT MAGNETS possess a the south pole, while magnetic force all on their own, and they the north pole. You will retain it permanently. This experiment kit find the corresponding has numerous permanent magnets in dif- letters — N for North ferent shapes, some with plastic coverings. pole and S for South These, too, are produced artificially, so they pole — written on the are stronger than natural magnetic rocks. magnets. →→→→→→ ←←←←←← magnet’s magnetic force is strongest are called its poles. Every magnet has two of them. In other locations, its magnetic force is much weaker. One pole is called the other is known as Magnets, Iron, and Poles | 19 CHECK IT OUT BAR MAGNETS… …are composed of a huge number of tiny magnets lined up in such a way that their magnetic effect is compounded. Iron also contains micromagnets of this type, but they are all jumbled up together in a way that cancels out their individual magnetic forces. If a magnet touches the iron, it lines up the micro-magnets so that the iron also turns into a magnet, at least temporarily. As soon as you take the magnet away, though, disorganization quickly returns. Curie temperature Iron, steel, and related materials lose their magnetic property at a certain temperature. This temperature is known as the Curie temperature after its discoverer, the French physicist Pierre Curie. Each material has its own unique Curie temperature. For pure iron, it is 766 degrees Celsius. If you heat iron above that point, it will no longer be attracted by a magnet, although it will regain its magnetism once you let it cool down below that temperature again. MAGNETIC CUSHIONS: Magnets can be stacked up with their repelling poles facing one another, as long as you make sure that they can’t slip to the side. The advantage of this kind of magnetic cushion lies in the fact that it lets you bring objects together in a practically friction-free manner. Magnets of this kind are used for sensitive technical instruments. The “Transrapid” magnetic levitation train also floats on a magnetic cushion, which enables it to reach speeds of up to 500 kilometers per hour without making very much noise at all. Note! attract Unlike poles ke poles ea ch other. Li r. he repel ea ch ot ✔ 20 Compass You must have noticed how a compass needle will move, and sometimes even dance wildly, when a magnet gets close to it. The compass needle is a very sensitive indicator of magnetic force. Now it’s time to investigate the reason for this… . Compass | 21 EXPERIMENT 15 Bloodhound for magnets YOU WILL NEED → all the magnets → compass → iron rod 1 HERE'S HOW 1. Place the compass on the table in such a way that its needle can move freely. Set the iron rod against the block magnet and position all the magnets as far away from the compass as possible. 2. Move the block magnet near the compass. Then, test all the other magnets as well. 2 3. Now move the iron rod, which had been lying alongside the block magnet, toward the compass. → WH AT ’S H A P P E N IN G ? etty far e magnet is pr Even when th points to it . le moves and away, the need weak nse relatively It can even se it s high es. Thanks to magnetic forc a thin is mounted on mobility — it it moves very ch a way that suppor t in su rces quite veals these fo ea sily — it re clearly. iron rod, readily to the It even reacts t. Af ter tually a magne which isn’t ac the powerful together with being placed rod retains a t, though, the block magne self. tism within it trace of magne 3 22 EXPERIMENT 16 The needle points to the pole YOU WILL NEED → all the magnets → compass 1 HERE'S HOW 1. Place the compass on the table in such a way that its needle can move freely. 2 2. Now hold the bar magnet close to the compass and pay special attention to which end of the needle points toward the magnet. 3. Now, turn the magnet around. 3 4. Perform the experiment with the other magnets as well. Hold the horseshoe magnet so that first the north pole and then the south pole is closer to the needle. → WH AT ’S H A P P E N IN G ? izes needle recogn The compa ss it . If d ar w turned to which pole is s red it s rn pole, it tu it ’s the south the ’s it if t; e magne end toward th d. en te ’s the whi north pole, it 4 Compass | 23 EXPERIMENT 17 Magnet on a string YOU WILL NEED → all the magnets → string → scissors HERE'S HOW 1 1. Tie a piece of string to the horseshoe magnet and hold the string so that both poles of the magnet are pointed down. 2. Now bring the bar magnet toward the horseshoe magnet, and move it so that first one pole is pointed toward the horseshoe magnet and then the other pole. Also try the same thing with the other magnets. → P E N IN G ? W H AT ’S H A P string , ing from the While it ’s hang onds sp re e magnet the horsesho edle. ne ss e a compa by turning lik ss pa m at the co That shows th a magnet. so needle is al 2 24 EXPERIMENT 18 The sewing needle shows the direction 1 YOU WILL NEED → polystyrene disk → bar magnet → compass → tape → magnetic needle from Experiment 6 → bowl → water 2 3 HERE'S HOW 1. Tape the needle to the center of the polystyrene disk. Fill the bowl with water and float the disk on the water. Be careful not to let the disk touch the sides of the bowl. 2. Now move first the north pole and then the south pole of the bar magnet toward the needle, and note when the pointed tip and when the eye of the needle is attracted. 3. Then place the bar magnet far away and pay attention to the direction the needle points after a few minutes. 4. Where does the needle point when the disk stops moving? Compare its position with that of the compass needle. 4 → P E N IN G ? W H AT ’S H A P point ways turns to The needle al if en ev — rection in the same di to sk di e en polystyr you turn the t en er ff di le in a point the need ion e same direct th ’s It direction. ts. in po le ed pa ss ne that the com a lf se ur ilt yo So you have bu . ss pa m simple co Compass | CHECK IT OUT History Still got it. Despite the existence of satellite navigation systems, the magnetic compass is still in use. GPS (Global Position Systems) can augment navigation with map and compass, but by no means replace it. In addition to its independence from any energy supply or electronics, determining your heading with a compass is a lot faster and more precise than using a GPS device. The compass needle… …is a magnet mounted in a way that lets it move easily. Its red end is the north pole, as you can see from the fact that it is attracted to the south pole of the bar magnet. So its white end must be the south pole. Apart from the traditional needle shape, the pointer can also take the shape of a complete disk or, in a ship’s compass, even the shape of a ball. Around the needle, you usually find an angle scale with compass points indicating cardinal directions such as north and south. You can rotate this scale so that the north pole of the compass needle actually points to “N” (north). That way, it’s easy to see exactly where the other directions lie. The compass is one of those inventions whose original creator is lost in the mists of time. Around 100 AD, the Chinese had a magnetic ladle with a handle that always pointed to the south. But it wasn’t until 900 years later that they used a compass needle to find their direction on the sea. In Europe, the ship’s compass with needle and compass rose was only introduced about 600 years ago — with farreaching consequences. This is what enabled brave European seafarers to venture out onto the open ocean. The age of exploration had begun, and Christopher Columbus crossed the Atlantic and sailed to America. 25 ✔ 26 Magnetic Force and Magnetic Fields You’ve probably been asking yourself what the iron powder in the plastic box is for. You will be amazed. You can use the powder to make a magnet’s force visible, since the powder accumulates wherever the magnetic force is strongest. What’s going on with the pretty iron powder patterns, what do their lines of force mean, and what do those lines have to do with Earth? You will learn about all these things and more in this chapter. Magnetic Force and Magnetic Fields | 27 EXPERIMENT 19 Hidden forces made visible YOU WILL NEED → bar magnet → block magnet → ball magnet → ring magnet → horseshoe magnet → box with iron powder HERE'S HOW 1. Take all the magnets in turn and hold them under the box with the iron powder. What do you observe? Can you recognize different patterns? → WHAT’S HA PPENIN G? The dif ferent magnets produce dif ferent iron powder patterns . You can use the iron powder to rende r the magnetic force visible. At the po les, which is where the magnetic force is strongest, the fine iron filings will even sta nd erect. You can see that particularly cle arly with the bar magnet and the horse shoe magnet. Since the block magn et ha s the strongest magnetic for ce, you can even use it to move the powd er back and for th inside the box. 1 28 EXPERIMENT 20 Who is stronger? YOU WILL NEED → all the magnets → compass → polystyrene disk → ruler 1 HERE'S HOW 2 1. Set the compass on the polystyrene disk. Place a bar magnet a few centimeters away, with its north pole pointing to the left side of the compass. 2. Now use the horseshoe magnet to check which side of the block magnet is the north pole. 3. Hold the bar magnet tight, and approach the compass with the block magnet from the top until the compass needle points in the middle between the two. It takes a little skill to get the two magnets in just the right position. 3 4. E xchange the block magnet for each of the other magnets in turn. How close does each of the other magnets have to be for the needle to be in the middle? → WH AT ’S H A P P E N IN G ? hich magnet s to decide w ha le ed ne e Th e greater int toward. Th it ’s going to po p magnet to e from which th ce an st di e th the bar le away from pulls the need e of the rc greater the fo magnet, the n use this ca u testing. Yo re u’ yo t ne ag m ea sy way to l setup as an experimenta different strengths of compare the magnets. 4 Magnetic Force and Magnetic Fields | 29 EXPERIMENT 21 Adding and subtracting forces YOU WILL NEED → bar magnet → 2 ball magnets → 2 ring magnets → polystyrene disk → compass 1 HERE'S HOW 1.Set the compass on the polystyrene disk and position the bar magnet as in Experiment 20. 2. Look for the north pole of the ball magnet. Hold the ball magnet at the distance that will make the compass needle remain halfway between the two magnets again. Continued on the next page. 2 30 EXPERIMENT 21 Adding and subtracting forces 3 HERE'S HOW IT CONTINUES 3. Now hold the ball tight and let the second ball magnet click to the first one, so they stick together by magnetic attraction. Where does the needle move? 4. You will have to move the two balls apart a little before the needle returns to its previous position. 5. Now take the two ring magnets. What happens when the second ring magnet turns its repelling pole toward the first ring magnet? (You will have to hold the two magnets tightly together to try this!) → P E N IN G ? W H AT ’S H A P another’s intensif y one Magnets can lly attracting n their mutua or strength whe The two ball ed together. an th poles are join er togeth are stronger ring magnets their if t Bu n. it s ow either one on eet, that lling poles m mutually repe e a bit. strength quit reduces their rces cancel e two poles’ fo Apparently, th nt . t to some ex te each other ou 4 5 Magnetic Force and Magnetic Fields | 31 EXPERIMENT 22 Muted magnetic force YOU WILL NEED 1 → bar magnet → horseshoe magnet → compass → iron rod HERE'S HOW 1. Set the bar magnet a little distance away from the compass. 2. Push the horseshoe magnet toward the compass from the top, and adjust the distance between magnets and compass so that the compass needle is in the middle again. 2 3. What happens to the compass needle when you slide the iron rod in front of the horseshoe magnet? 3 → P E N IN G ? W H AT ’S H A P fond e magnet is so Apparently, th s it d that less of of the iron ro t from ou s ad re sp e magnetic forc e, it s ef fect is it ­­— therefor weaker. e of iron is So when a piec e poles of a attached to th eaker pears much w magnet, it ap n it s ide than whe from the outs . poles are free 32 EXPERIMENT 23 Compass needle as bloodhound 1 YOU WILL NEED → bar magnet → compass HERE'S HOW 1. Place the bar magnet on the table and start by moving the compass very slowly around it in a tight circle. 2. Then continue moving it around the compass in larger and larger circles. Keep your eye on where the needle is pointing as you do this. 2 → WH AT ’S H A P P E N IN G ? le und, the need With each ro me sa rding to the behaves acco net ag m ts as if the principle. It ac es lin ed by lots of were surround ch hi one pole, w coming out of it e space around th pa ss through r he ot e rn back to th and then retu as n es are know pole. These lin of force. es magnetic lin pa ss ch as the com A magnet, su ient or to y tr ways needle, will al with d ne ig al at it is it self such th force. these lines of Magnetic Force and Magnetic Fields | 33 EXPERIMENT 24 Lines of force made visible YOU WILL NEED → all the magnets → box with iron powder HERE'S HOW 1. Place the box with iron powder on top of each of the magnets in turn, as you did in Experiment 19. 2. This time, though, pay special attention to the patterns that form after shaking and knocking the box holding the iron powder. Keep the magnet pressed tightly against the box as you do this. You may have to try it a few times before you get a pretty pattern. → WH AT ’S H A P P E N IN G ? field, each In a magnetic s into particle turn on individual ir s ve t that beha a tiny magne le. compa ss need a similarly to er by th ge ts stick to These magne les, po ng attracti their mutually tic ne ag m ns in the and form chai es lin e th parallel to field running of force. ly ea sy are particular These chains e horseshoe to see with th e of ing in the shap magnet, runn e one pole to th an arch from ts, ne ag m r he ot e other. With th you t, e block magne especially th es of e how the lin can clearly se s. from the pole force emerge 34 EXPERIMENT 25 The magnetic force of Earth YOU WILL NEED → all the magnets → polystyrene disk → compass → bowl → saucer → water → magnetized needle from Experiment 6 HERE'S HOW 1. Fill a bowl with water as you did in Experiment 28, place the bar magnet on the polystyrene disk, and let the disk float in the bowl. Check the orientation of the magnet with the compass. Carry out this experiment with the other magnets as well. If they are too heavy for the polystyrene disk, simply use another floating base, such as a saucer. → WH AT ’S H A P P E N IN G ? s so t quickly turn The bar magne “N” an h it w d marke that the end le the the north, whi is pointing to uth. The ints to the so other end po se ts, and of cour other magne well, as le ed zed ne your magneti northemselves in a also orient th to a n in response south directio h. covering Eart magnetic field 1 Magnetic Force and Magnetic Fields | CHECK IT OUT 35 ✔ EARTH’S MAGNETIC FIELD For centuries, it was a complete mystery why a magnetic needle pointed to the north or south. Scientists rightly asked what the rotation of Earth might have to do with magnetism. Were there, for example, gigantic magnetic mountains at Earth’s poles? Or might the North Star, which could be seen above the North Pole, be responsible? Today we know that Earth acts as if there were a giant bar magnet hidden inside it. But Earth’s magnetic poles don’t exactly match the rotational poles. Instead, they are a few thousand kilometers away. Between these magnetic poles, there is a powerful magnetic field stretching across the entire globe. This is what your magnets and all magnetic compasses react to. Earth’s magnetic field isn’t actually produced by a permanent magnet, but by enormous electric currents circulating deep beneath the surface in its metallic core. MAGNETIC MOUNTAINS C In fact, you can’t detect any particularly strong magnetic field at Earth’s magnetic poles. And there’s nothing very unusual about the landscape there. The supposed magnetic mountains — in the Middle Ages, people believed in the existence of a magnetic mountain that could pull the iron nails out of ships that passed by it — belong to the realm of fairy tales. What is interesting is that the magnetic field’s lines of force enter the magnetic poles in a vertical direction, so the needle of an appropriately designed compass will point straight down. 36 | Magnetic Force and Magnetic Fields CHECK IT OUT Ma g net i c so MAGNETIC FIELD ✔ Earth’s axis of rotation ut h p ole Geographic north pole Ma g ne t ic field r th p ole tching The lines stre le are po to le from po tic called magne e. rc fo lines of c no Note Geographic south pole net i The field is especially strong close to the poles, but as you move away from the magnet it quickly gets weaker. Ma g We can neither see nor feel a magnetic field, but iron and other magnets will react to it by being attracted, repelled, or rotated. lines The lines depicted here are just a model. But you can picture a magnet as producing a countless number of lines arranged tightly together. This invisible force of a magnet is known as its magnetic field. Earth’s axis of rotation WHICH POLE IS NORTH? C This is how you can picture Earth’s magnetic field. Compass needles orient themselves relative to the magnetic lines of force and thus point in a north-south direction. And in the drawing above, the artists didn’t make an error in putting the magnetic south pole next to the geographic north pole! The compass needle, remember, is a little magnet. The end pointing to Earth’s north pole has long been called the north magnetic pole. That applies to all magnets — even your bar magnet will rotate such that the N side is turned toward the north. But since, as you know, north and south poles always attract each other, the magnetic pole near the geographic north pole is logically a magnetic south pole. Electromagnetism | Do electric current and magnets have something in common? As you know, a compass needle reacts to magnetic fields. Will it also react to electricity? You can use the wire included in the kit to assemble a small electromagnet, with its magnetic force supplied by electric current. Then you can test its powers… Electro- magnetism 37 38 EXPERIMENT 26 Magnetism from electricity 1 YOU WILL NEED → wire → compass → 1.5-volt battery → scissors → tape → sheet of letter-size paper HERE'S HOW 2 1. Place the compass on the paper and wait for the needle to orient itself. 2. Guide the wire across the compass in such a way that it runs parallel to the needle. Secure it in this position with tape. 3. Hold the ends of the wire by their plastic insulation and briefly touch their exposed parts to the battery contacts. Watch the compass needle as you do this. 3 1.5 V CAUTION! Only connect the wire to the battery very briefly, for just about one second. The powerful current will heat up the wire and the battery. You could burn yourself with the hot wire, and the battery could get damaged by the heat or quickly run out. → WH AT ’S H A P P E N IN G ? ar ts e electricity st As soon as th e th e, ir w h the to flow throug side. e th to s le jerk compa ss need Electromagnetism | 39 EXPERIMENT 27 Electromagnet with intensified effect YOU WILL NEED 1 → wire → compass → horseshoe magnet → 1.5-volt battery (AA) → scissors → tape → sheet of letter-size paper HERE'S HOW 1. Wrap the center part of the wire five times around one arm of the horseshoe magnet and carefully pull the magnet out of the coil of wire. 2. Position the coil above the compass. Tape the wire to the paper as shown in the illustration. Then, as you did in the last experiment, tap the wire ends against the battery terminals. Keep your eye on the needle. → P E N IN G ? W H AT ’S H A P is time. ally moves th The needle re xt to it , e you have ne The more wir s to atically it jerk the more dram larger coil, with it s the side. The ire, seems to quantity of w ef fect of the intensif y the t. electromagne 2 40 EXPERIMENT 28 Intensifying the magnetic force even more 1 YOU WILL NEED → iron rod → wire → compass → 1.5-volt battery (AA) → tape → sheet of letter-size paper HERE'S HOW 1. Disassemble the wire again and create a narrow coil out of it by winding it about 15 times around the iron rod. 2 2. Tape the coil to the paper and set the compass in front of it. Let the current flow briefly. How does the compass react? 3. Now push the iron rod into the coil and briefly let the current flow again. 3 → WH AT ’S H A P P E N IN G ? react edle doesn’t At first , the ne r all, te rongly — af particularly st far ty et ire is still pr most of the w re . The iron co away from it e e power of th intensifies th t, t quite a bi electromagne even with a , though. Now een distance betw considerable le ed ss, the ne coil and compa ngly. ro reacts very st Electromagnetism | 41 EXPERIMENT 29 Exchanging poles YOU WILL NEED → setup from Experiment 28 1 HERE'S HOW 1. Repeat the last experiment. Pay attention to which end of the compass needle points to the coil. 2. Then place the compass at the other end of the coil, and briefly switch on the current. Which end of the compass needle points to the coil now? 2 3. Repeat this experiment, but first reverse the battery terminals so the current flows the opposite direction through the wire. What are the positions of the needle this time? 3 → WH AT ’S H A P P E N IN G ? w really does The current flo agnet, e coil into a m transform th sa tromagnet ha and this elec like a st ju le po h ut north and a so ss as the compa bar magnet — when y shows. And needle clearl te ws the opposi the current flo the ugh the coil, direction thro s of the magnetic pole ell. t switch as w electromagne 42 Gigantic electromagnet at the nuclear research center in Geneva, Switzerland Electromagnetism The relationship between magnetism and electricity was first discovered around 1820, using the very same experiment with wire and compass that you tried on page 39. Scientists, who had previously thought of these two things as being completely different, were highly surprised. But there had already been a few clues before then. People had often noticed that a compass needle could become reversed after lightning struck a ship. Today we know that the lightning’s powerful magnetic field reversed its magnetization.. Electromagnetism | 43 CHECK IT OUT ELECTROMAGNETS C have ✔ lots of technical and industrial uses — namely, wherever particularly powerful magnets Galvanometers are needed. Recyclers, for A coil of wire wound example, use electromagnets around a compass (along attached to cranes to lift heavy with more coils of a pieces of iron. To let them go, thinner wire) is called a all they need to do is turn off galvanometer, a device the current. long used as a sensitive gauge for electric current. Electromagnets are also used ( Historic mirror galvanometer in speakers, electric motors, and power plant generators. One of the world’s largest electromagnets is found at the European Organization for Nuclear Research lab in Geneva, Switzerland, with a core made of 64,000 metric tons of steel. (photo on p. 42) ELECTROMAGNETS are only magnetic as long as current is flowing through them. When that happens, it creates a magnetic field around the wire. When you turn off the flow of current, the magnetic field disappears ­— so electromagnets can be switched on and off. 44 GAMES with Magnets You can take advantage of magnetic effects to play some fun games. A little patience, speed, or skill may be needed. Fishing with magnets is a classic game, played for decades by children in many parts of the world. It’s most fun if you play the games together with a friend, so you can teach them everything you know about magnets. Games with Magnets | 45 EXPERIMENT 30 Every ball in its place 1 YOU WILL NEED → all the ball magnets → multicolored paper strip → paper → pen 2 3 HERE'S HOW 1. Place the paper strip flat on the table. 2. Position the ball magnets as shown in the illustration. 3. Now, taking turns, each player moves either the red or the green ball one hole at a time toward the center of the strip. At first, of course, it will be easy, but sooner or later the balls will start sensing one another’s magnetic force, with a growing risk that they might clack together. The winner of the round is the last one to have set a ball into a hole without making it clack together with the ball in the center. That player can assign himself or herself the point total written next to the corresponding hole. After about ten rounds, each player adds up his or her points. Whoever ends up with the most points is the winner. 46 EXPERIMENT 31 Magnetic fishing 1 YOU WILL NEED → bar magnet or horseshoe magnet → plastic chips → tape → string → wooden cooking spoon → colored felt-tip pens → tall box → paper → glue stick → permanent marker 2 HERE'S HOW 1. Decorate the box with sheets of paper with pictures of fish drawn on them. 2. Tape the bar magnet to the string and tie the other end of the string to the end of the cooking spoon. 3 3. Spread the plastic chips across the bottom of the box. 4. Now you can start your fishing competition. Taking turns, each player lowers the magnet into the box (without looking into it, of course), and fishes out one or more chips. The winner is the one who catches the most chips. Or, you could use the permanent marker to write different point totals on each of the chips, and the angler with the highest point total wins. 4 Games with Magnets | 47 EXPERIMENT 32 Invisible attraction HERE'S HOW YOU WILL NEED → block magnet → ball magnet → large sheet of paper → thick felt-tip markers → heavy cardboard → scissors → glue stick → watch with second hand or stopwatch → heavy book 1. U se the felt-tip markers to draw a thick, winding line with lots of loops on the paper. Mark a starting point and a finishing point. Glue the paper to the cardboard. 2. Set the ball magnet on the starting point and guide it along the curving line toward the finishing point by moving the block magnet against the underside of the cardboard. Variations a) Along with a few friends, see who can navigate the “race track” the fastest. Deduct points for errors. b) You can increase the level of difficulty by increasing the distance between cardboard and magnet, for example by using a thick book. That will make it harder to keep the ball from rolling off in its own direction. 1 2 48 | Games with Magnets EXPERIMENT 33 Magnetic snake and magnetic axle 1 YOU WILL NEED → all the ball magnets → block magnet → all the ring magnets → iron rod HERE'S HOW 1. Arrange the ball magnets into a colorful line and set them on the table. 2. By holding the block magnet a slight distance away, you can make your ”snake” move. Alternate the ends of the bar magnet to pull the snake or push it away, and to make it move its “head” (the ball at the front). 2 3 3. For the magnetic axle, stick two pairs of ring magnets together and arrange the pairs with their mutually repelling poles facing each other. Insert the iron rod through their center holes. Now pull the pairs away from each other until they are at the ends of the rod. 4. Now you can use the block magnet again to move your wheeled axle. 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