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How the Strength of a Magnet Varies with Temperature

Difficulty
Time Required Average (6-10 days)
Prerequisites None
Material Availability Readily available
Cost Low ($20 - $50)
Safety Adult supervision highly recommended. Use proper caution when transferring or holding magnets at extreme temperatures. See the Procedure for details.

Abstract

Physicists sometimes study matter under extreme conditions. For example, think of the emptiness of interstellar space vs. the unimaginable crush of pressure at the center of a neutron star, or an object dipped in liquid nitrogen vs. the tiles on the space shuttle during re-entry. Here's an experiment on permanent magnets in "extreme kitchen" conditions that you can try at home.

Objective

The objective of this project is to determine whether the temperature of a magnet affects its strength.

Credits

Sabine De Brabandere, PhD, Science Buddies
Andrew Olson, Ph.D., Science Buddies

Sources

This project is based on:

Cite This Page

MLA Style

Science Buddies Staff. "How the Strength of a Magnet Varies with Temperature" Science Buddies. Science Buddies, 22 Feb. 2016. Web. 25 May 2016 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p025.shtml>

APA Style

Science Buddies Staff. (2016, February 22). How the Strength of a Magnet Varies with Temperature. Retrieved May 25, 2016 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p025.shtml

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Last edit date: 2016-02-22

Introduction

Magnets are fascinating; they are fun to play with and can even create artistic creations. Figure 1, below, gives you a glimpse of what you can expect during this science project.

Magnets allow to create fascinating and beautiful creations, like this pattern of paper clips that are stuck to one big  magnet.
Figure 1. Magnets allow you to create fascinating and beautiful creations, like this pattern of paper clips that are stuck to one big magnet.

Scientists need magnets that function in extreme conditions, like in the cold emptiness of space. In our day-to-day life, magnets experience more-moderate extremes, like the freezing winter temperatures in Alaska or the unbearable heat of a summer day in Death Valley, California. Would a magnet still function well in those conditions?

It is important to note there are several types of magnets. This science project only deals with permanent magnets, magnets that always retain their magnetic characteristics. In other words, they always create a magnetic force (magnetic pull or push) on magnetic material in their vicinity. Do you think these magnets are always permanent, or are there exceptions at extreme temperatures?

In everyday language, we usually refer to magnets, and materials that are attracted to magnets, as magnetic. Technically, these materials are called ferromagnetic. Not all metals are ferromagnetic. Try to pick up a copper penny or a piece of aluminum foil with your magnet. Does it work? The most common ferromagnetic metals are iron, nickel, and cobalt. They are special because at the microscopic level, they contain many tiny magnetic domains. Each magnetic domain is like a tiny magnet with a north and south pole. Normally, the tiny magnetic forces created in those domains point randomly in all directions, so they cancel each other out, and as a result the material will not exert a magnetic push or pull on other ferromagnetic materials. However, when the material is placed in a strong magnetic field, the material gets magnetized, and all of these tiny magnetic fields line up, creating an overall larger magnetic field, as illustrated in Figure 2, below. To learn even more about magnets, check out the Science Buddies Electricity, Magnetism, & Electromagnetism Tutorial.

In ferromagnetic material, tiny magnetic domains act like tiny magnets. They can be oriented randomly in different directions (left) or they can line up and combine to create a large magnetic force field (right).
Figure 2. In ferromagnetic material, tiny magnetic domains act like tiny magnets. They can be oriented randomly in different directions, canceling each other out (left) or they can line up and all point in the same direction (right). When they line up, they combine and create a large magnetic force field, which allows the magnet to exert a magnetic force on other ferromagnetic materials.

Now, what would happen if you heated up the magnet? Scientists define the temperature of a material as a measure of random movement of atoms or molecules (the tiny particles the material is made of) within the material. Even when you see a solid block of metal, the atoms within this solid block are constantly vibrating back and forth. They move a little less when the block is cold, and a little more when the block is warm. Because heating up the block increases the random motion within the metal, would it also affect the alignment of magnetic domains? If so, an increase in the temperature of a magnet would tend to decrease its strength. In fact, each ferromagnetic material has a Curie temperature (named after Pierre Curie), above which it can no longer be magnetized. For some metals, like iron, the Curie temperature is over 1,300°C! Your oven at home might get as hot as 260°C, so obviously 1,300°C is out of the question for a science project. But what happens to the strength of a magnet over a more approachable range of temperatures, like from the temperature of your freezer (about −20°C) to the temperature of boiling water (+100°C)? In this science project, you will find out.

Terms and Concepts

  • Permanent magnets
  • Magnetic force
  • Ferromagnetic materials
  • Magnetic domain
  • Temperature
  • Equilibrate

More advanced students may also want to study:

  • Diamagnetic materials
  • Paramagnetic materials

Questions

  • What is an object's temperature actually a measure of?
  • What happens on an atomic level when you heat up a substance?
  • How could heating up or cooling down a magnet affect the alignment of its magnetic domains?
  • How could you measure the strength of a magnet?

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Materials and Equipment

  • Large ceramic magnet like the 4 ½ inch diameter ring magnet available from Amazon.com or Grainger.com.
    • Note: It is advised not to use neodymium, or "rare earth" magnets, as they might not give clear results for this test.
    • Best results are obtained with a large magnet, like the suggested 4 ½ inch diameter, 3/8 inch thick magnet listed above.
    • Avoid using very thick magnets, as these will take a while to heat or cool throughout.
    • Temperature stabilized magnets are less prone to show permanent loss in magnet strength when repeatedly heated. Reversible losses (the loss you study in this project, where the magnet recovers its strength when it returns to its original temperature) are not eliminated by magnet stabilization. It is advised to use a temperature stabilized magnet for this science project.
  • Tongs for holding magnets (preferably plastic)
  • Thick heat-resistant glove or oven mitts that fit over your hands (not pot holders)
  • Standard #1 metal paper clips (2 boxes of 1,000 each)
    • Note: Plastic paper clips will not work, vinyl coated paper clips are fine.
  • Flat surface or plate at least 2 inches wider than the diameter of your magnet
  • Digital scale with 0.1 g increments. A digital scale that would be suitable (the Fast Weigh MS-500-BLK Digital Pocket Scale) is available from Amazon.com.
  • Small bowl or container, to be used as a "measuring boat" in which to collect paper clips and measure their weight
  • Thermometer (minimum range −30 to 110°C); available from Amazon.com
  • Freezer
  • Ice cubes (about 3 trays worth)
  • Large plastic bowl (your magnet needs to fit in the bowl)
  • Water
  • Stove or hot plate for heating water
  • Pot in which to heat water. Choose a pot that is not ferromagnetic so your magnet is not attracted to the pot. Your magnet needs to fit completely into the pot.
  • Lab notebook

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Experimental Procedure

Preparing Your Work Area and Tools

Caution: Here are some general safety guidelines you should read before you do this project.
  1. Always use tongs or thick, insulated gloves for handling magnets at extreme temperatures.
  2. Practice handling the magnet using tongs and thick, insulated gloves at room temperature before heating or cooling your magnet.
  1. You will test your magnet at four different temperatures:
    1. Approximately −20 °C (the temperature of your freezer)
    2. 0°C (the temperature of a water ice bath)
    3. Approximately 20 °C (room temperature)
    4. 100 °C (the temperature of boiling water)
  2. You will use the amount of paper clips that the magnet can pick up as a measure of its strength.
    1. Because your magnet might pick up quite a few paper clips, you will not count the number of clips, but will use their total mass, expressed in grams (g) as your unit of measurement.
  3. Copy the following data table in your lab notebook. It will be used to record your measurements.
  Freezer Ice/Water Bath Room Boiling Water
Temp (°C)     
Trial 1 (g)     
Trial 2 (g)     
Trial 3 (g)     
Trial 4 (g)     
Trial 5 (g)     
Average (g)     
Table 1. Make a data table like this one in which to keep track of measurements. You will record the measured temperature in the second line and the measured mass of paper clips picked up by the magnet for each trail in the following lines.
  1. Practice measuring the strength of the magnet:
    1. It is important to perform exactly the same procedure for each trial. You will practice and optimize your procedure in this step.
    2. With your magnet at room temperature, follow the procedure described in Measuring the Magnet Strength, below, and measure the magnet strength (the amount of paper clips picked up) a couple of times. Note that small variations in your measured results are to be expected. Scientists call these statistical fluctuations. Your job is to pay attention to ways you might introduce variations and find ways to eliminate those as much as possible.
    3. Here some ideas of ways you might introduce variations to get you started:
      1. Bringing the magnet down sideways for one trial and flat for another introduces variations in your measurements. Bring the magnet down the same way each time.
      2. Picking the magnet up with insulated gloves for some trials and bare hands for others can introduce variations in your measurements. You might push off more paper clips when using insulated gloves. Use your gloves for all trials, even the trials at room temperature.
      3. Different ways of piling the paper clips can introduce variations in your measurement. Create a flat-top pile—at least 2.5 cm (approximately 1 inch) wider than your magnet—for each trial.
  2. Once you feel confident that you can make reliable measurements, go to the section Taking Measurements at Various Temperatures, below.

Measuring the Magnet Strength

  1. Create a pile of paper clips like the one shown in Figure 3, below. You can do this on a flat surface (as in Figure 3) or on a plate (as can be seen in Figure 4, below). The pile needs to be at least 1 inch wider than your magnet on each side of the magnet. Make sure the top of the pile of paper clips is flat.
pile of colorful paper-clips
Figure 3. A flat pile of paper clips will be used to measure the strength of a magnet.
  1. With your insulated gloves on, hold your magnet above the pile.
  2. Lower the magnet down slowly until it rests in the middle of the pile of paper clips, as shown in Figure 4, below.
pile of colorful clips on magnet
Figure 4. The magnet rests on a flat pile of paper clips that were originally placed as a flat pile on a plate or flat surface. The number of paper clips it picks up when removed is a measure of the strength of the magnet.
  1. Now, slowly remove the magnet from the pile. Ideally, you should not add or remove any paperclips stuck on the magnet with this movement. It is ok, though, if you need to push off some paper clips that are stuck to the magnet to remove the magnet from the pile, or to pinch off additional paper clips, as long as you make sure you use the same movements with every measurement. Try not to pick up extra paper clips that are not stuck to the magnet though.
  2. Zero out your scale so it indicates 0 g when the container you are using to measure (your measuring boat) is on the scale. Tip: If the scale you are using does not have a feature to zero it out, you will need to first weigh the measuring boat so that you can subtract this mass from the total when you weigh the paper clips.
  3. Remove all the paper clips picked up by the magnet from your magnet and gather them in your measuring boat. Tip: If not all the paper clips fit in your measuring boat, measure half of the clips, than measure the second half and add up the results.
  4. Record the mass picked up by the magnet in your lab notebook.

Taking Measurements at Various Temperatures

Important: One more note before you start your measurements at different temperatures. Whenever you cool or heat your magnet to a desired temperature, it is very important to allow the magnet to equilibrate to the test temperature before measuring the magnet's strength at that temperature. Give the magnet at least 20 minutes to attain a uniform temperature when it is immersed in water and 30 minutes when it is in open air. This will ensure that not only the surface, but also the inner core of the metal, attains the desired temperature. The Introduction (see section on domains) will give you a clue on why this is so important.

Freezer Test

  1. Place your magnet in the freezer for about 30 minutes.
  2. Place your thermometer in the freezer.
  3. Prepare your pile of paper clips as described in the section Measuring the Magnet Strength.
  4. Take the magnet out, measure its strength (as described in the section Measuring the Magnet Strength) and put it instantly back where you got it from for this test so it is ready for your next trial.
  5. Leave your magnet for at least 10 minutes to equilibrate with the test temperature again.
  6. Repeat steps 3–5 four more times for a total of five trials.
  7. Take your thermometer out of the freezer and record the temperature of your freezer in the data table in your lab notebook. Take your magnet out of the freezer.

Ice/Water Bath Test

  1. In a large plastic bowl, prepare a bath of water and ice cubes.
  2. Place your magnet in the bowl. Make sure it is completely submerged.
  3. Leave it in the ice/water bath for at least 20 minutes, evaluating intermittently if the bath needs extra ice. Note: Since the room is warmer than your ice/water bath, heat will flow from the room to the bath, melting your ice. To keep the temperature of the bath at 0°C, you might need to replenish the ice.
  4. Repeat steps 3–6. While you do so, keep an eye on the ice/water bath, making sure it always contains some ice.
  5. Use your thermometer to measure the temperature of the ice/water bath and record your findings in your data table. Take your magnet out of the water/ice bath.

Room-Temperature Test

  1. Let your magnet and thermometer sit out at room temperature for at least 30 minutes.
  2. Repeat steps 3–6. Note: In this case, you do not need the additional 10 minutes between trials, as the magnet stays at room temperature all the time.
  3. Use your thermometer to measure the room temperature and record your findings in your data table in your lab notebook.

Boiling Water Test

  1. Put a pot with plenty of water on the stove and bring it to a soft boil.
  2. Use tongs to put the magnet in the water. You will also use the tongs to take the magnet out of the water. Leave the magnet in the water for at least 20 minutes to equilibrate.
  3. Repeat steps 3–6. While you do so, keep the water at a soft boil.
  4. Use your thermometer to measure the temperature of the boiling water and record your findings in your data table in your lab notebook. Take the magnet out of the water, let the water cool and safely dispose it.
  5. You are finished measuring and can start analyzing your results.

Analyzing Your Data

  1. For each temperature, calculate the average mass the magnet picked up. You do this by adding the masses picked up by the magnet for Trial 1, Trial 2, Trial 3, Trial 4, and Trial 5 for a given Temperature (e.g. freezer temperature) and divide this total by the number of trials, here 5. Record the average in the last line of your data table.
  2. Make a graph of magnetic strength, as measured by mass picked up (y-axis, the vertical axis), vs. temperature (x-axis, the horizontal axis).
    1. Tip:You can make a graph by hand or make a graph using a computer program, such as Create a Graph, and print it out.
  3. Look at your data table and graph, and try to draw conclusions from your results.
    1. Does magnetic strength increase, decrease, or stay the same over the temperature range you tested?
    2. Can you explain these results with what you learned about ferromagnetic materials in the Introduction?
    3. Could you conclude your tested magnet will still function properly under extreme kitchen temperatures? Would it be safe to extrapolate these findings to more common sizes of ceramic kitchen magnets?

Troubleshooting

For troubleshooting tips, please read our FAQ: How the Strength of a Magnet Varies with Temperature.

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Variations

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Frequently Asked Questions (FAQ)

If you are having trouble with this project, please read the FAQ below. You may find the answer to your question.
Q: Why do my measurements vary? My magnet seems to pick up different amounts of paper clips for each measurement, even if I keep the magnet at the same temperature.
A: Variations in your measurements are normal. Even if the strength of the magnet at a specific temperature is constant, the measured mass of paper clips picked up by the magnet will vary from trial to trial. These variations are mainly caused by slight changes in how you perform the measurements. If you think about it, will the paper clips always be in exactly the same position as you lower the magnet? Could that influence how many the magnet picks up? Will you always hold the magnet exactly the same way, and could that influence how many are picked up? These small changes result in a different number of paper clips being picked up by the magnet, or in other words, varying measurements.

Although you cannot eliminate these variations, you can do your best to reduce them. Here are some tips:

  • Practice your measurement procedure and while you do so, look for details that might influence your measurement. Be sure to include these details in your measurement procedure (see next point).
  • Write down a clear measurement procedure. You might be surprised how easy it is to forget details like whether or not you kept your hand on the magnet when the magnet rested on the paper clips. A written detailed procedure will clarify any doubts.
  • Use the same materials for each measurement: the same heat-resistant glove or oven mitts, the same scale and measuring boat, et cetera.

Once you have reduced the variations as much as possible, the following steps can help you find a trend and increase your confidence in an accurate average measurement:

  • Do not compare individual measurements of magnet strengths at different temperatures. Calculate averages first and then try to see a trend in the average values. As a comparison, to detect a trend in height of first- and second-grade students, would you blindly pick a first grader and compare this person's height to the height of one randomly picked second grader? No, because there is a chance you picked an exceptionally tall first grader or a relatively small second grader. The average of the height of a sample of first graders and the average of a sample of second graders would give you a better idea of the general height and trend. The same is true for your magnet strength measurements; trends are easier to spot in the average values.
  • Make a larger number of repeated measurements; this will generate an average that is, in general, closer to the true value. The procedure asks for five trials, but you could increase it to eight or ten measurements at each temperature. To understand this point, think about how it would impact the average height data of first- and second-grade students. An average of the heights of students of a class, or even several classes, will generally provide a more trustworthy average than an average of the heights of only five students.
Q: I expect to see a trend in my average values, but I cannot see one. Am I doing something wrong?
A: As a first step, evaluate if you allowed enough time for the magnet to acquire the test temperature throughout (not just at the surface, but all the way to the middle of the magnet material) before measuring the magnet's strength at that temperature. Did you give the magnet at least 20 minutes to attain a uniform temperature when it is immersed in water and 30 minutes when it is in open air? Did you place your magnet back in the freezer, ice water, or boiling water between measurements? Did your ice water always have ice in it?

If you did, the effect might be smaller than your measurement accuracy. The question on varying measurements might help you take more accurate measurements.

You could also increase the temperature range over which you take measurements. An oven can help you heat the magnet to higher temperatures. If you do so, be sure to stay well within the temperature range for which your magnet was stabilized. When you expose your magnet to extreme temperatures (cold as well as warm), it will get damaged and show permanent loss. The question on reversible and permanent loss and the explanation of what can weaken your magnet will help you understand this better.

Q: I have read about permanent and reversible loss in magnet strength due to temperature variations. What is the difference?
A: When you heat a magnet, its strength can decrease. This is called a loss in magnet strength, or demagnetization of the magnet. There are two distinct cases. If after bringing it back to normal conditions, the magnet returns to its original strength, the loss is called reversible. If after bringing it back to normal conditions, the magnet strength is only partially recovered, scientists speak about permanent loss. A manufacturer is usually able to undo the permanent loss, but special treatment of the magnet is needed to regain its original strength. With reversible loss, it automatically regains its strength when brought back to normal conditions.

Think of a rubber band. If you stretch it a little, it will return to its original shape, the stretch was reversible. If you stretch it a lot, it might shrink again but it will remain longer than it originally was, the stretch is permanent.

You are studying reversible loss in this science project.

Q: My magnet suddenly seems much weaker. What happened?
A: Here are a couple of reasons that could explain your observation:
  • Did you heat or cool your magnet to extreme temperatures? Exposure to extreme temperatures (like putting it on dry ice or heating it to over 400°F) can cause permanent loss in magnet strength. The previous question explains the difference between reversible and permanent loss.
    If your magnet acquired permanent loss, this experiment might help you understand permanent and reversible loss better. Take new measurements with the weaker magnet and use only the new values to explore reversible loss. You can also compare the measurements before the exposure to extreme temperatures to the measurements after the exposure to explore permanent loss. It is important to remember not to combine measurements from before the exposure to measurements taken after the exposure. It is like combining measurements of two different magnets.
  • Other (less likely) factors that affect magnet strength are storage or holding it close to other strong magnets. A soft drop of a recently manufactured magnet will most often not cause a loss in strength, but hard drops might. If any of these apply, follow the solution offered under extreme temperature exposure.
  • You might be observing variations in your measurements, or you might have unknowingly changed your measurement procedure slightly. The question on varying measurements can help you understand variations in your measurements better, and provide ideas on how to reduce them as much as possible.
Q: The magnet specifications states it is "temperature stabilized." Can I still use this magnet for this project?
A: Yes, you should use a temperature-stabilized magnet for this science project.

Temperature-stabilized magnets are less prone to show permanent loss in magnet strength when repeatedly heated. Reversible loss (the loss you study in this project) is not eliminated by magnet stabilization. The question on permanent and reversible loss explains the difference between these two types of loss in magnet strength.

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