The Science Notebook
Magnetism, Magnets and Electricity - Pt. 2

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 On this page...
Making a Compass Using an Induced Magnet 
Making a Better Compass 
Yet Another Compass
A Closer Look at the Compass
Making an Electromagnet 
Using an Electric Current to Magnetize a Nail
Observing How an Electric Current Affects a Magnetic Compass
Making a Galvanometer
Making an Electric Motor 
Studying a "Hobby" Motor
An Electric Generator 
How Efficient Is A Generator?

Making a Compass Using an Induced Magnet


Materials Needed: Small bowl; steel needle (or pin); magnet; compass; disposable foam coffee cup.

Procedure:   Magnetize the needle or pin by stroking it with a magnet several times just as you did with the nail.  Cut the bottom from a foam coffee cup leaving just a little bit of the side, and make a small notch on each side of the bottom so that the needle can rest on top of the circle without moving. Place the needle or pin so that it rests in the notches.  Next, fill the bowl with water and carefully float the needle and foam in the bowl.  Allow the needle to settle down.

Place the compass a few feet away and allow the compass needle to settle down as well.  Make sure the magnet you used isn’t near either the compass or the magnetized needle.

What To Look For: In which direction is the needle pointed?  What about the compass?

What Happened: You have already learned that the needle in a compass is really a small bar magnet.  So is the magnetized needle.  The compass needle is able to turn freely.  The magnetized needle is able to turn freely because it floats on the foam circle.  However, because  the lid is completely free to float, it may drift to the side of the bowl, and so would not make a very good compass for practical use.  But you can use what you have learned so far to make a better one...


Making a Better Compass


The compass you will make in this experiment is similar to the one you just made, but with one big improvement.  In the last experiment, you probably noticed that the cup bottom and needle would move to the edge of the bowl and it could no longer turn freely.  You can fix that by adding a straight pin, a piece of a soda straw and a little modeling clay to make a pivot for your compass.

Materials Needed: Small bowl; steel needle (or pin); magnet; compass; Styrofoam coffee cup; modeling clay; straight pin; soda straw.

Procedure:   Cut the bottom from a foam coffee cup and prepare it just as you did in the last experiment.  From the same side as the notches, push the straight pin through the center of the cup bottom and push it all the way through except for the head.  Place just a little modeling clay around the pin on the underside to hold the pin in place.  Next, cut a 3 cm (1 in) piece from the soda straw.  Then, place a small lump of clay in the bottom center of the bowl.  Place one end of the straw into the lump of clay so that the straw is sticking straight up as shown.

Magnetize the needle or pin just as you did before.  Place the needle or pin in the notches.  Next, fill the bowl with water so that it completely covers the straw and carefully place the foam bottom and needle over the straw so that the pin coming from the underside of the bottom goes inside the straw.  There should be just enough water in the bowl to allow the bottom and needle to float freely.  The pin inside the straw will act as a pivot to prevent the needle and cup bpttom from drifting away

Allow the needle to settle down and check the direction of the needle with that of a compass as you did in the last experiment.  Now turn the cup bottom a couple of turns and let it go.  What happens?

What Happened: Just as a real compass needle turns about on a pivot, the needle of the homemade compass was able to turn around freely but was prevented from floating to the side of the bowl by the straw and pin pivot.  While you couldn’t very well take this compass with you to the woods or on a ship, you could use it to perform the other experiments in this book that call for you to use a compass.

Going Further: Can you use what you have learned to make a more usable compass?


Yet Another Compass

If you tried the experiment using tha bar magnet as a compass on the Magnetism 1 page, you already know that a bar magnet suspended and alllowed to swing freely will act as a compass.  (If you missed that one, you can click HERE to view it.)  In the experiments above, you have seen the same thing with an induced magnet allowed to move freely in water.  In this experiment, you will use an induced magnet suspended in air as a compass.

CAUTION!  Always use sharp objects such as knives or scissors with adult supervision only!  Hold any sharp point away from your body, particularly your eyes.

Materials Needed: Steel clothes hanger; (You can test it with a magnet.); wire cutter; permanent magnet; compass; nylon fishing line or string; fishing swivel; paper, scissors; tape; empty box or other support.

Procedure:  Have an adult to cut a 30 cm (12 in) section of wire from the bottom of the clothes hanger.  Use the permanent magnet to make an induced magnet of the clothes hanger wire as described in THIS EXPERIMENT on the Magnetism 1 page.  (Will open in a new tab or window.) 

Cut a piece of paper 3 cm (1 in) by 6 cm (2in).  Tape the two 3 cm (1 in) ends together to form a teardrop shape.  Punch a small hole in the middle of the taped part almost at the top.  Hook the fishing swivel through this hole. Tie a 30 cm (12 in) piece of fishing line or string to the other end of the swivel.  Tape the other end to the inside of a cardboard box as shown.  Slip your wire induced magnet through the paper loop and balance it.  Once the magnet is balanced, let it go until it stops swinging.

While you are waiting for the magnet to stop swinging, move the compass some distance away from the hanging magnet, and let it settle down as well. Note the direction in which the compass is pointing.  Now note the direction the wire magnet is pointing.

(NOTE: If you don’t have a fishing swivel, you can simply tie your line or string directly to the paper.  However, without the swivel, the magnet may spin around a bit, especially if you had to use string, and you may need to give it a few minutes to stop swinging. )

What To Look For: If all was done properly, the wire magnet should be parallel to the compass needle.  You should  see that both the magnet and the compass line up north to south, and the magnet behave just like a compass. 


A Closer Look at the Compass


Materials Needed: A compass.

Procedure:   Place the compass on a table or other flat surface and allow the needle to stop swinging.  Carefully turn the compass so that the end of needle which points north is lined up with the “N” on the compass rose or the direction ring.  The compass rose is the card under the needle with the directions printed on it.  The direction ring is a ring around the edge of some compasses that may be turned.  If your compass has a rose, it may look like a star, or it may simply be a series of numbers and marks that show N, S, E, and W, or go from 1 to 360, or both.

What To Look For:  As you have already seen, the compass needle is a small bar magnet.  Unless it is very close to another magnet or a large object made of iron or steel, it will line itself up in a north-south direction.  By lining up the needle with the “N” on either the compass rose or the direction ring, you can not only tell which direction is north, you can also identify all the other directions as well.

What Happened: Scientists believe that the core of the earth is made up of a mixture of iron and nickel metals.  The outer part of this core is thought to be liquid, while the inner core is believed to be solid.  In a way that is not completely understood, the core behaves like a giant magnet with a north and a south pole.  The poles are located many miles below the surface of the earth, near the actual north and south poles of the earth.  The actual poles are called the geographic poles. As you have already seen, any magnet, if left to turn freely, will align itself with the earth’s magnetic field.  The north pole of the magnet will always point north, while the south pole will always point to the south.  However, since the magnetic poles of the earth are not located at exactly the same points as the geographic poles, a compass may or may not point exactly north, depending on exactly where the compass is located.

Going Further: Look up compass in an encyclopedia or online to learn more about how it works.


Making an Electromagnet

We said that electricity and magnetism were related.  In this experiment, you will see how electricity can be used to make a magnet.

Materials Needed: Insulated copper wire (You can use wire from an old Christmas light string or or almost any other covered wire); iron nail (not galvanized); homemade battery holder with 2 AA, AAA, C or D cells; two wire connectors of your choice; homemade switch (This is optional, but will make the experiment much easier to do.); wire from your circuit experiments; small staples or paper clips.

Procedure:    Starting about 5 cm (2 in) from the end of the insulated wire, wind about 30 turns around the nail.  Leave the same amount on the other end.  (If the wire doesn’t want  to stay in place, you can tape it down by wrapping a little tape around each end.  Carefully strip about 1 cm (½ in) of the insulation off of each end of the wire.

Next, assemble the circuit shown below.  If you are using the switch, assemble it like this:


If you are not using the switch, leave a gap between the wires where the switch would go.

Press the switch (or touch the two wires where the switch would be together), and bring the coil near a few loose staples.  What happens?

IMPORTANT!  Do not leaves the switch closed or the wires connected for more than a few seconds as this will quickly drain your batteries!  Remember, this is a “short” circuit!

Open the switch or disconnect the wire.  Now what happens to the staples?

What Happened:   When the switch was closed, electricity began to flow through the wire.  The flow of electricity through the wire created a magnetic field that caused the coiled wire and nail to behave like a magnet.  However, when you opened the switch or disconnected the wire, electricity could no longer flow and the magnetic field disappeared.  (You may see that the nail still acts as a magnet even after you open the switch or disconnect the batteries.  We’ll see why in just a little bit.)
 
When a magnet is made by electric current flowing through a wire it is called an “electromagnet”.  However, you may remember that when you send an electric current through a wire that this creates a “short” circuit that will quickly drain the batteries.  That’s why you don’t want to leave the batteries connected for too long!

Going Further: What effect does adding more turns of wire have on the strength of the electromagnet?  How about fewer turns?

NOTE: You will use this same setup to do the next experiment.


Using an Electric Current to Magnetize a Nail

Materials Needed:  Setup from the last experiment.

Procedure: Turn the electromagnet back on by closing the switch or reconnecting the wires for a couple of seconds.  Open the switch or disconnect the wire so that current cannot flow.  Next, unwrap the wire from the nail.

Now bring the nail near some staples.  What happens?

What To Look For: The staples should be attracted to the nail, although the attraction may be very weak. 

What Happened: When the electricity flowed through the wire, it not only created a temporary magnetic field, it also caused the iron atoms to line up and create a weak magnetic field.  When current stopped flowing, the iron atoms remained in place and a very weak magnet was created.  This is another example of induced magnetism, but in this case, electricity is used to create the field instead of a permanent magnet.

Going Further: Can you strengthen such a magnet by leaving it connected longer?  (Don’t try this for too long.  Remember this is a “short” circuit which will drain your batteries very quickly!)  Can you demagnitize this magnet using heat or by rapping the nail?


Observing How an Electric Current Affects a Magnetic Compass


Materials Needed:   Insulated copper wire; compass; one AA, AAA, C or D cell.

Procedure:   Wrap four or five turns of wire around the compass.  Strip the insulation off the ends of the wire.  Turn the compass so that the wire is lined up with the compass needle.

Hold one end of the wire to the bottom of the cell.  At the same time, touch the top of the battery with the other bare end for just a second.  What happens?

What To Look For: The needle should move from underneath the wire.

What Happened: You have already seen that a magnetic field is created when a current passes through a wire.  The compass needle, which is a magnet, responds to that magnetic field by lining up with it.  This setup can be used to detect small electric currents.  It also helps us to understand how a motor works, as we will see later.

Going Further: What happens if you use fewer turns of wire?  What happens if you simply place a wire with electricity flowing through it across the compass?


Making a Galvanometer


In the last experiment, you actually made a galvanometer, which is a simple device used to detect small electric currents.  In this experiment, you will make a more permanent  and sensitive galvanometer.

Materials Needed: Compass; magnet wire; corrugated cardboard; tape.  (Magnet wire is thin copper wire that is coated with enamel.  It is available from Radio Shack®.  If you can’t find magnet wire, you can use insulated wire, but it will be a little thicker.)

Procedure: Cut a small rectangle of cardboard.  The shorter side should run along the corrugations, and should be about 1 cm (½ in) longer than the compass.  The longer side should be at right angles to the corrugations and should be about 2 cm (1 in) wider than the compass.

Next, fold the cardboard along the corrugations about 1 cm (½ in) on each side.  Cut a small “v” shaped notch into the other two sides in the center.  Tape the compass to the top of the cardboard with the “N” and “S” of the compass rose lined up with the notches.

Leave about 30 cm (1 ft)  of wire, and wind 50 turns around the notches.  When you have finished winding, leave about another 30 cm (1 ft).  You can tape the wire coil on the underside to hold it in place.  Place another piece of tape from one side of the cardboard to the other on the underside to make the galvanometer steady.  Strip about 1 cm (½ in) insulation from each end of the wire.

To test your galvanometer, line it up so that the wire coil is lined up with the needle.  Touch the wires to the ends of a cell, and observe the needle.  Reverse the wires.  What happens?

What Happened: When you touched the wires to the cell terminals, the needle swung out from under the wire and probably went at right angles to the wire.  The swing may have been strong enough to cause the compass needle to spin.  When you reversed the leads, the needle again swung out, but this time in the opposite direction.  The magnetic field created by the electric current is at right angles to the flow of the current through the wire.

Going Further: Find a battery that appears to be “dead” and test it with your galvanometer.  You may be surprised to find that it will deflect the needle at least a little.  Even though the dead battery may not be producing much current, the galvanometer can detect even the small amounts of current being produced.


Making an Electric Motor




This project began as a motor is based on the “Beakman” motor from the TV show, “Beakman’s World”, and works on the same principle.  However, this version uses wood screws instead of paper clips for support to make the motor a little more durable.  It also takes a hint from a motor experiment developed by Home Science Tools, using ink from a permanent marker as an insulator. You can also add a switch to prevent the battery from accidentally running down.

Materials Needed: Small piece of wood, about 6" square; 2 2x10 flat head (not Phillips) screws; 2 clothespins; insulated wire (or you can substitute two clip leads for the clothespins and wire as shown in the photo); homemade switch (optional, but a good idea); D cell; small rectangular magnet (Radio Shack® # 64-1877 or similar); 22 gauge magnet wire; rubber band; tape; aluminum foil; toilet paper tube; sand paper; permanent marker.

Procedure:   Starting about 9 cm (3 in) from the end of the magnet wire, wrap 7 turns of wire around the toilet paper tube.  Measure off another 9 cm (3 in) and cut the wire.  Carefully slip the wire off the paper tube while holding the wire turns together so that they don’t come loose.  Loop the two ends of the wire around the coil tightly a couple of times to secure the coil as shown in the diagram.

Next, using sandpaper, completely remove the insulation off of both ends up to the edge of the coil. This next step is important!  Placing the coil on a flat surface, use the marker to completely cover one side of the wire only.  


Screw the two wood screws into your board 12 cm (4 in) apart as shown.  You should be careful to screw them in as straight as possible, and you only need to screw them in enough to hold them securely for the time being.  Both should be screwed in to the same depth, and the slots on both heads should line up in a straight line.

Cut a 15 cm (6 in) piece of insulated wire and remove ½ cm (1/4 in) of insulation from each end. Tape one end over one end of the D cell.   Tape the wire from one end of the homemade switch over the other end, and secure the wire to the cell using a rubber band, just as you did for the homemade battery holder.

Fasten the free wire ends coming from the D cell to the one of the screws near the base by wrapping the bare wire with foil and clamping the wire and foil to the screw with a clothespin.  If you want to add a  homemade switch; insert it as shown in the diagram,  

While making sure that your switch is off, place the ends of the coil into the slots on the screw heads.  Give the coil a slight spin to make sure it spins freely.  If not, adjust the screws and the coil as required.  Then, center the magnet directly underneath the coil, and spin the coil.  The coil should not touch the magnet as it spins.  A gap of about ½ cm (1/4 in) inch is good.  If you need to raise or lower the coil, adjust the screws up or down as needed.

Once you’ve adjusted everything, close the switch and give the coil a spin.  It should begin to turn on its own.  If not, try spinning the coil in the opposite direction.  If it still doesn’t spin on it’s own, slowly turn the coil until you see it attracted to the magnet.  You may need to shift the magnet around a little.  If it is not attracted to the magnet somewhere along the way, check your sanding to make sure you removed the insulation properly.  If it doesn’t spin easily, you may need to readjust the coil so that it does.  Once you have the motor working properly, you can bend the wires on each end to keep the motor from flying off of the screw heads.

What Happened: As the coil rotated, the side that was half insulated with marker ink turned so that the half with no insulation came in contact with the metal screw making a complete circuit.  This created an electromagnet which was attracted to the bar magnet below it.  When the coil was pulled down to the magnet, the insulated side of the wire touched the screw head which broke the circuit.  Inertia kept the coil spinning until the bare wire contacted the screw and the circuit was completed again.  The coil was again attracted to the magnet.  As long as the battery was hooked up, the cycle kept repeating and the motor continued to spin.

Going Further: There are many ways of experimenting with this motor.  Changing the shape of the coil or the number of turns of wire used, or adding another cell are just a few of the things you can try. 


Studying a “Hobby” Motor


You have seen how a motor works by creating an electromagnet that is switched on and off.  Hobby motors, like those used in model cars and other toys, have electromagnets that switch on and off.  These motors are available at Radio Shack ® and at many hobby shops.  With the help of an adult, you may even be able to salvage one or two from old toys.
Materials Needed: 1.5 to 3 volt hobby motor (Radio Shack ®  #273-223 or equivalent); two alligator clips (Radio Shack ® #270-374 - These are optional, but very helpful); insulated wire; aluminum foil; 2 AA, C or D cells; homemade battery holder; homemade switch; small iron or steel object such as a pin or staple.

Procedure: Examine the hobby motor.  You should see two small metal tabs with holes in them.  There are the “terminals” where the wires are connected to the motor.  Move your small iron or steel object around the outside of the motor.  Is this object attracted to the motor at any point?

Remove ½ cm (1/4 in) of insulation from each end of a 15 cm (6 in) piece of wire.  Make a homemade battery holder using this wire and the two cells.  Connect one of the wires of the homemade switch to one end of the battery holder.  Make sure the switch is open.  Connect the other switch wire to one of the terminals on the motor by inserting the bare wire into the hole, wrapping it with a bit of aluminum foil, and clamping it in place with an alligator clip.  If you don’t have an alligator clip, strip about an inch of insulation from this wire, run it through the hole, twist tightly and wrap a bit if aluminum foil around the wire.  Squeeze the foil tightly. Do the same thing with the wire from the other side of the battery holder.  Hold the motor firmly and close the switch.

What To Look For: The motor should begin to run.  If it doesn’t, carefully recheck all of your connections.

What Happened: You should have discovered that some part of the motor appears to be magnetic when you held the iron or steel object close to the motor.  This is because most hobby motors have one or more magnets inside.  The magnets inside the hobby motor serve the same purpose as the magnet on the homemade motor. 

By connecting a battery (two cells) to the motor, you assembled a circuit that provided electricity to several electromagnets in the motor.  Having several electromagnets allows the motor to spin very rapidly.  As we will see in the next experiment, something else very interesting is going on.

Going Further: Notice the direction in which the motor is spinning.  What happens if you reverse the wires on this motor?


An Electric Generator 


When a magnet passes through a coil of wire, the magnetic field produces an electric current. This should not be surprising, since we have already seen that electricity flowing through a coiled wire produces a magnetic field.  Remember the galvanometer?  And since a motor has one or more coils which are turning past one or more magnets, it should not surprise you that a motor may also be used to generate electricity.

Materials Needed: All the materials from the previous experiment; a second hobby motor; a small piece of wood, about 15 cm (6 in) square; a light and holder from the Christmas light set; modeling clay; an unused eraser from a new pencil; aluminum foil; two additional alligator clips (optional); a straight pin.

Procedure: Assemble the motor circuit from the last experiment.

Using a pair of pliers, pull an eraser from the end of a new pencil.  Push a straight pin through the center from the top of the eraser all the way through the bottom.  Keep it as straight as possible.  Remove the pin. 

Push the shaft of your second motor into the hole at one end of the eraser and slide it about halfway through the eraser.  Push the shaft of the first motor through the other end of the eraser so that the two shafts are joined.  Place both motors on the board and brace them with four pieces of modeling clay as shown. 

Next, close the switch to test the setup.  The friction between the eraser and the shafts should cause the shaft of the second motor to turn when power is connected to the first motor.  You may need to adjust the position of your motors and their braces so that the motors turn as smoothly as possible.

Finally, attach the two ends of the lamp holder with lamp to the two terminals of the second motor in the same way as you attached the battery and switch to the terminals of the first motor.  Now turn on the first motor.  What happens?

Be sure to leave this setup in place for the next experiment.

What To Look For: The lamp should light.  If it does not, check it’s connections to the second motor.  Also, check your bulb to insure that it is not burned out and try again.  Pay very close attention to the brightness of the bulb for the next experiment.

What Happened: The second motor is not electrically connected to the circuit powering the first motor.  However, as the first motor spins, it causes the second motor to spin since the shaft of the first motor is turning the second due to the connected shafts.  As the second motor spins, it’s coils pass through magnetic fields created by the permanent magnets inside the motor.  This produces electricity that lights the bulb.  The second motor is being used as a generator.

Going Further: Now that you know what is happening, perhaps you can come up with other ways of generating electricity.  Connect a light to a single motor with another eraser fastened to the shaft. Turn a bicycle upside down and have a friend turn the pedals while you place the side of the shaft of the motor against the outside of the turning wheel.  Can you cause the shaft to turn by friction and produce enough electricity to light the bulb?   


How Efficient Is A Generator?


In the last experiment, you made a small generator.  Now, you’ll get some idea of just how efficient your generator actually is.

Materials Needed: (For the most accurate results, all of these materials should be from the last experiment.)  Light bulb and holder; switch and battery holder with batteries used to power the first motor; two clothespins; aluminum foil; alligator clips (optional) .

Procedure:   You should have observed the brightness of the bulb as lighted by the generator in the last experiment.  If you didn’t notice it before, connect the light to the generator again and observe the brightness of the bulb.

Now, using the aluminum foil and clothespins or alligator clips, connect the light directly to the battery holder and observe its brightness.  Is there a difference?

What Happened:  Your two cell battery should be producing about 3 volts when it powers the motor that turns the generator.  However, the output of the generator will be  somewhat less, since some of the energy used to power the first motor is lost as heat or friction, and additional energy is also lost due to friction created by the spinning of the second motor.  Therefore, not all of the energy will go into generating electricity.  Another way of saying this is that the generator is not 100% efficient.

When you connect the light directly to the battery, you don’t have these losses.  All of the available energy from the batteries goes to lighting the bulb so it is brighter.

Going Further: If you are looking for a good science project, you might want to compare the efficiencies of a generator powered by two cells used to light a bulb, and two cells which light the bulb directly.

Start with four fresh cells and using two of them, construct a generator as before.  Using the other two cells, construct a light circuit using the same arrangement as in this experiment. Make sure you use the same size bulbs, and keep everything in the two setups as nearly alike as possible. Compare the brightness of the two bulbs over time.  What do you conclude?  You may also want to compare how long two batteries will last when used to power the generator to light the bulb versus how long two batteries will last lighting the bulb directly.


If you have gone through all the electricity and magnetism pages, congratulations!  If not, cruise on over to the Experiments page.  There you'll find links to these pages and much, much more!


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