The Science Notebook
Magnetism, Magnets and Electricity - Pt. 1

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MAGNETISM AND ELECTRICITY
Observing the Poles of a Bar Magnet
Demonstrating that a Compass Needle is a Magnet
Identifying the North and South Poles of a Magnet Using a Compass
Using a Magnet as a Compass
Observing Magnetic Fields Using Powdered Iron 
Observing Magnetic Fields Using Powdered Iron in Three Dimensions
Making a Device to Observe Magnetic Fields in Three Dimensions 
Measuring a Magnet's Relative Strength
Making a Magnet Using Induced Magnetism
Using Heat to Demagnetize a Magnet
Another Way to Demagnetize a Nail


MAGNETISM AND ELECTRICITY

You have probably played with magnets at some point and are already at least a little familiar with them.  But you may not know that magnetism and electricity are related.  In these experiments, we will study some of the properties of magnets and magnetism, and we will also see how a magnet can be used to produce electricity.


Observing the Poles of a Bar Magnet


Materials Needed:  Two bar magnets.  (NOTE:  Some magnets are labeled “N” and “S” on the ends.  These markings designate the “poles” of a magnet.  However, if your bar magnet is not marked, that doesn’t mean it doesn’t have poles.  We will learn how to mark and identify poles later.)

Procedure:  Place one of the magnets on a smooth surface such as a table.  Now bring one end of the other magnet to one end of the magnet on the table and observe what happens.  Next, separate the two magnets, and bring the other end of the magnet you are holding to the same end of the magnet on the table.  Again, watch what happens.  Repeat the process for the other end of the magnet on the table.  Also, if the ends are marked, note what happens as you bring the marked ends together.

What Happened:  Every magnet is surrounded by an invisible field called an “magnetic field”.  If two magnets are brought together, their fields affect each other. When the ends of the two magnets were brought together one way, they were attracted to each other.  However, when you reversed one of the ends, the magnets repelled or pushed each other away. If you were using marked magnets, you should have seen that the “N” and “S” ends attracted one another, but that the “S” and “S” ends or the “N” and “N” ends repelled each other.  On magnets that are marked, the “N” end is commonly called the north pole and the “S” end is the - you guessed it - south pole of the magnet. And there is a very good reason why these ends are called the north and south poles as we will see.

Going Further: Try bringing your two magnets together in different places to see whether there are other places where they attract and repel.


Demonstrating that a Compass Needle is a Magnet


Materials Needed: Small bar magnet; compass; tape; pen or pencil.   

Procedure: Identify which end of the compass needle points north. It is sometimes marked with a dot or an “N”, but if you are not sure, get some one to help you. With the magnet several meters (yards) away from the compass, allow the compass needle to settle down until it points north.

Now, bring one end of the bar magnet to the compass. Note which end of the compass needle swings toward the magnet. Move the magnet several meters (yards) away from the compass.  Turn the magnet around, and bring this end of the magnet toward the compass. Now which end of the needle swings toward the magnet? 

What To Look For: You should see that the end of the compass needle that points north is attracted to one end of the magnet, and the end that points south attracted to the other end of the magnet. If your bar magnet has is marked “N” on one end, and “S” on the other, you should notice which end is attracted to the north pointing end of the compass and which end is attracted to the south pointing end.

What Happened: As you have already seen, a magnet will attract one pole of another magnet, but it will repel the opposite pole of that same magnet. A compass needle is a weak magnet and it has north and south poles.  The end of the compass needle that points north is the north pole of the compass needle magnet, and the end that points south is the south pole.

Going Further: How far away can you move the bar magnet and still attract one end of the compass needle or the other.


Identifying the North and South Poles of a Magnet Using a Compass

Two experiments back, you saw that a magnet has north and south poles. Then, in the last experiment, you learned that a compass is a magnet, and that the end of the compass needle that points north is the north pole of that magnet, while the other end is the south pole of that magnet. We can combine these two pieces of information to use a compass to help us mark and identify the poles of an unmarked bar magnet.

Materials Needed: Unmarked bar magnet (such as may be found at Radio Shack ®. If your bar magnet is marked, have someone to tape over the markings on each end with masking tape so you can’t see them.); compass; masking tape; pencil or pen.

Procedure:   If someone else has not already done so, put a small piece of masking tape on either end of the bar magnet. Then, bring one end of the unmarked magnet near the compass. If the south pointing end of the needle swings toward the magnet, label that end of the magnet  “N”. If the north pointing end of the needle swings toward the magnet, label that end “S”. If you used a marked magnet that was taped over, see if your labels agree with the marks.

What Happened: You already know that the compass needle is a small bar magnet. You also should remember that the end of the compass needle which points north is the north pole of the magnet and the end which points south is the south pole.  Ordinarily, when a compass is not close to another magnet, it is attracted to the earth’s magnetic field.  (More about that later!)  However, once you bring another magnet close to the compass needle, the strength of your magnet is much greater than the earth’s magnetic field, and the compass needle is attracted to it.  You have also seen that opposite poles attract when two magnets are brought close to one another. Since opposite poles attract, if the north pole of the compass swings toward the end of your magnet, the end it is attracted to would be the south pole.  Likewise, if the south pole of the compass is attracted to the end of the magnet, that end of your magnet is the north pole of that magnet.

Going Further: See whether there is any change when you turn your magnet over.  Some magnets that look like bar magnets, don’t have the poles on the narrow ends.  If you have such a magnet, can you figure out where the poles are?  How about with a round, circular, or other odd shaped magnet?


Using a Magnet as a Compass


We have seen that a compass needle is a bar magnet.  If that is true, can an ordinary bar magnet be used as a compass? Let’s find out.

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: Marked bar magnet (The one you marked in the last experiment is perfect!); compass; nylon fishing line or string; fishing swivel; paper, scissors; tape; low lying tree limb or other support.

Procedure: 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.  Tie the other end of the line to a low tree branch or other support as shown. Slip the 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 each pole of the bar 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 twist 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 north pole of the magnet should be pointed north and the south pole should be pointed to the south, just like the compass. If not, make sure the compass and magnet are far enough apart that they don’t attract one another, and try again. If the south pole of your magnet is pointed north, and you labeled it yourself, check to make sure that you labeled it correctly.  If you are using a bar magnet that has been improperly stored, it can sometimes reverse poles as well.  In any case, you should  see that both the magnet and the compass line up north to south, and the magnet behave just like a compass. 


Observing Magnetic Fields Using Powdered Iron


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:   Several magnets of different sizes and shapes; white paper;  powdered iron.  Most school science labs have powdered iron (also called iron filings) which you can borrow.  They won’t be “used up” so you should be able to return all of the powdered iron when you are done.  If you can’t get some powdered iron, take a piece of steel wool and unroll it.  Using a sharp pair of scissors, have an adult help you to cut tiny pieces by cutting across the strands of the unrolled steel wool.

Procedure:   Place a magnet underneath under a sheet of paper.  Sprinkle a little powdered iron over the top of the paper.

What To Look For:  You should see a pattern of lines form on the paper running from one pole to the other.  The pattern will vary depending on the shape of the magnet and its position under the paper.  (A bar magnet will produce a pattern something like the one shown above.)

What Happened: There is a force surrounding the magnet called a magnetic field.  The particles of iron are attracted to that field, allowing you to see at least part of the field.  The field is strongest at the poles of the magnet, so most of the powdered iron will concentrate there.
 
Going Further: Try moving the magnet around underneath the paper to see different parts of the field.


Observing Magnetic Fields Using Powdered Iron in Three Dimensions 

In the last experiment, you saw the magnetic field in only one dimension - a flat surface.  As you moved the magnet, you could see different parts of the magnetic field. But the magnetic field surrounds the field in three dimensions, and in this experiment, you will be able to see a portion of this field in three dimensions.

Materials Needed:   Several magnets of different sizes and shapes; powdered iron (iron filings); plastic sandwich bag. 

Procedure:   Place one of the magnets inside the plastic sandwich bag.  Flatten the bag to get as much air out of the bag as possible, and seal it.  Now dip the magnet into the powdered iron.  After you have finished, remove the magnet by turning the bag inside out so as not to get powdered iron on the magnet.  Powdered iron on the magnet won’t hurt anything, but it will be difficult to remove. 

Repeat this experiment with different magnets.

What To Look For:  You should see the powdered iron concentrated near the poles.

What Happened: You were able to see the magnetic field. In three dimensions.


Making a Device to Observe Magnetic Fields in Three Dimensions 


Materials Needed:   Several magnets of different sizes and shapes; baby oil or mineral oil; clear flat plastic bottle; powdered iron or steel wool clippings.  (See last experiment).
 
Procedure:   Find a clear plastic bottle with as nearly flat sides as possible.  The bottle that the baby or mineral oil comes in is often nearly flat on at least two sides.  Remove the  labels and fill the bottle completely with oil.  Add about 1/4 tsp of steel wool clippings or powdered iron to the oil.  Screw the cap on tightly and shake well to spread the particles.

Place one of the magnets against the flat side of the bottle.  What happens to the iron or steel?  Shift the magnet around and see if the pattern changes.  Shake the bottle and repeat with different magnets.

Add a little more powdered iron if needed to see the pattern clearly, but be careful not to add too much.

What Happened: You were able to see the magnetic field, in three dimensions because the thickness of the oil kept the particles of iron from lumping together.  This experiment and the last one both show that a magnetic field is not flat.  Instead, it surrounds the magnet in all directions. 


Measuring a Magnet's Relative Strength

Materials Needed: Several different magnets; several dozen small pins, paper clips, safety pins, tacks, or other small objects made of iron or steel.  (You should use all of the same kind of object, and whatever you use must be attracted to a magnet.)

Procedure: Make a table like the one shown below, but without the numbers. 

Dip one of the magnets into the metal objects you have chosen (we’ll assume you chose pins) and pick up as many as you can.  Remove the magnet and count the number of pins you picked up.  Write down the number in the table.  Remove the pins and repeat.  Do the same thing with all the other magnets.

Number of Pins Picked Up

First Trial Second Trial Average
Magnet # 1 18 16 17
Magnet # 2 21 20 20.5
Magnet # 3 7 11 9


What To Look For: You’re trying to determine which magnet in your group is the strongest.  By seeing which magnet attracts the most pins, you are measuring the relative strength of the magnets.  In other words, you are comparing the magnets to each other.  In the example above, magnet # 2 is the strongest of the three.

If you set a standard for measuring the strength of a magnet in “pins”, you might say that magnet #1 has an average strength of 17 pins, since it picked up an average of that many pins.  You have now created a new standard for measuring a magnet’s strength, the "pin." By using this standard, you have now made an absolute measurement of a magnet’s strength.


 Making a Magnet Using Induced Magnetism


Materials Needed: Small iron or steel object such as a small nail (or a pin or needle); a magnet; a few small iron or steel staples.

Procedure: Test your nail to make sure it is iron or steel by using the magnet.  If it isn’t attracted to the magnet, you can’t make a magnet from it.  Also, you should not use a galvanized nail. (Galvanized nails are coated with zinc and usually have a gray color. If the nail has a little rust on it, it probably is not galvanized.)  Test the staples to make sure they will be attracted to a magnet also.

Next, rub the magnet along the nail about 20 strokes in one direction only.  Do not rub back and forth.  After you have done this, bring one end of your metal object to a few of the staples.  What happens?

What To Look For: The nail should now act like a magnet and attract the staples, although the attraction will probably not be very strong.

What Happened: Rubbing the magnet against the nail in one direction caused the iron atoms in the object to line up and create a weak magnetic field, which made the nail behave like a magnet.  You had to rub in one direction to get the atoms to all line up in the same manner.  If you had rubbed back and forth, the atoms would not have lined up as well, and the magnetic field would probably not be as strong, if one was created at all.  Magnetism created in this manner is called induced magnetism.

Going Further: Can you make the nail a stronger magnet by rubbing longer?  How about harder?  How can you tell?  Can you make a stronger magnet by using a larger nail? Can you use what you learned in the last experiment to measure the strength of your magnet?


 Using Heat to Demagnetize a Magnet

CAUTION!  Always be careful to follow all safety precautions when using fire, and use with adult supervision only!  Keep your candle in an aluminum pie pan, and keep the flame at least three feet away from anything that can burn, unless otherwise instructed.

Materials Needed:   Candle or alcohol lamp with safety pan; nail magnet from the last experiment; a pair of pliers or tongs; staples from the last experiment

Procedure:   Hold the nail magnet in a candle flame using a pair of pliers.  Move the nail through the flame so that all parts of the nail are heated.  Remove the nail from the flame and allow it to cool thoroughly!  Once it has cooled, try to pick up the staples again.

What To Look For: Does the nail magnet pick up the staples?  If so, is it stronger or weaker than it was?

What Happened: If you heated the nail long enough, the nail was no longer magnetic.  Heat causes the atoms of iron in the nail to vibrate, and as they do, they no longer line up to produce the magnetic field.  The nail may still have attracted some of the staples, but you should have noticed that the attraction was much weaker after the nail was heated.

Going Further: Can you re-magnetize the nail after it has been heated?


Another Way to Demagnetize a Nail

Materials Needed: Nail magnet; staples.

Procedure:   Make another nail magnet as described in Experiment 3-31.  Test it using some staples to see how strong it is.  Next, hit the nail as hard as you can several times on a hard surface such as a rock or sidewalk.  Using the staples, test your nail magnet again.

What To Look For: Does the nail magnet still attract the staples?  If so, is it as strong as it was before?

What Happened: Just as heat caused the molecules of iron to vibrate, hitting the nail jarred the molecules out of line and destroyed or weakened the magnetic field.

Going Further: Can you re-magnetize the nail after it has been demagnetized in this manner?


Now you know the basics of magnetism, but to understand how magnetism and electricity are related, you need to check out Magnetism, Magnets and Electricity - Pt. 2


"The Science Notebook"  Copyright 2008-2014 - Norman Young