Magnets and Magnetic Fields

Experiment with Magnets

Magnets:

First begin by grabbing two magnets that you might find lying around home.  If they are fridge magnets, or similar, then place the two faces towards each other about 10 cm apart, and slowly bring them close together.

1. Do you feel any force, push or pull, interacting between the magnets?  Describe what you notice.  Be sure to comment on the distance between magnets.

2. Now, flip ONE magnet to the other face, and repeat the experiment, starting about 10cm away from each other and then slowly bringing them together.  Do you notice a push or pull?  Explain and again be sure to comment on distance.

3. As you may have heard, all magnets are dipoles, meaning they have two opposite ends which create opposite physical characteristics.  We refer to them as North and South ends of a magnet.  One could call them positive and negative, like electrical charges and they would have the same effect in nature, so north and south are really just arbitrarily chosen designations.  A standard picture one might have of a magnet is depicted below.

4. Notice the two ends of this horseshoe are labelled N and S for north and south.  One could say they are the same magnitude, but opposite directions, if you want to think of them in terms of vectors.  Similar to electric charges, in magnetism, opposites attract, and likes repel. So when you brought two poles of the magnet together that were the same, they repelled each other, and when you brought two poles of the magnet together that were different, they attracted one another

5. Now take one of the magnets and bring it close to a metal paperclip.  What do you notice?  Repeat this procedure, only be sure to hold the paperclip in your hand.  Comment on the effect of distance.

6. Assume you just used the “north” end of the magnet in #3 (though we don’t know this for certain).  Repeat #3 with the “south”, or opposite, end of the magnet and write down your results below.

7. You might begin to ask yourself, why do opposite ends behave the same way with a metal paperclip!?  That seems strange.  With electrical charges, oppositely charged particles  behaved differently, didn’t they?!

In the case of magnets, they have opposite characteristics, with respect to each other but in some cases, they behave similarly.  In the case of attracting a paperclip, paperclips have some iron in them, and so they have “magnetic properties”.  Entire research fields are dedicated to the study of magnetic properties, but we will simply state matter is made up of tiny magnets.  When a material has magnetic properties, and it is close to a strong magnet, the tiny magnets align just like the magnet near them!  An image of this is depicted below.

Case Study on Magnetic Properties of Metals

Imagine the image above is a block of iron and the arrow tips are the direction of North on the tiny magnets that the iron block is made of. In the left image, the block is isolated, not near any magnets.  So the tiny magnets inside the iron, magnetic domains, which it is created from, are randomly aligned.  The right picture shows the iron near a strong magnet, which will cause the magnetic domains to have a similar orientation as the big magnet which is nearby.

a. Notice we are careful to state “nearby” in the explanation above.  Why is that?  

b. Now repeat the procedure for #3 and #4 with the aluminum beverage can.  Write a summary of your results below.

c. Many people often associate ALL metals as being heavily attracted to magnets, but that is simply NOT the case.  Many metal materials have no iron and therefore when their magnetic domains align, similar to iron, they feel a very weak attraction to the magnet.  Aluminum is one such metal.

d. The next portion requires you to use a cell phone/tablet and a free magnetic field sensor app.  All smartphones/tablets have a magnetic sensor.  Please download one of the free apps below to install on your phone or tablet, and proceed to the next question.

e. If none of these apps works for, just search your app store for “free magnetic field sensor” and you will most certainly find one.

f. To illustrate magnetic domains better, bring your phone/tablet close to one side of the magnet with the compass app open.  Make note of which end of the compass is pointing to that side, and then bring the compass to the other side of the magnet, and make note of which side of the compass is pointing towards that side.  Illustrate your results in a sketch or photo below.

g. The compass needle should always point to the magnetic north pole of the earth, but when it is near the magnet, the needle “re-aligns” in the same orientation as the magnet, where the north pole of the needle touches the south pole of the magnet, and vice-versa for the south pole of the needle. 

Now, you might be asking yourself, what is it about the magnet that causes the magnetic domains in metals, and compass needles, to align in the same way?  The answer to that question is the magnetic field!  

Using your compass app, your magnet, the internet, and your textbook, sketch out a magnetic field for two different shaped magnets.  You may not have magnets of two different shapes, hence why you are welcome to use your textbook and the internet to find another one.  Verbally describe how each magnetic field would affect a compass in different regions of the field.  For example, “to the left of the horseshoe magnet, the north end of the compass needle would point downwards”.  Make 5 such statements for 5 different locations around the magnets.  Insert your sketches and descriptions below.

Hopefully, given any shaped magnet and a compass, you would now be able to visualize the magnetic field around the magnet.  Not an easy thing to do as magnet shapes can be quite unique, depending on the use of the magnet.  Always keep in mind that traditionally we say that the magnetic fields lines exit the north pole and enter the south pole.