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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, 18 Nov. 2014. Web. 25 Nov. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p025.shtml>

APA Style

Science Buddies Staff. (2014, November 18). How the Strength of a Magnet Varies with Temperature. Retrieved November 25, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p025.shtml

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Last edit date: 2014-11-18

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.

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?

Bibliography

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Materials and Equipment

  • Large ceramic magnet like the 4 ½ inch diameter ring magnet available from Amazon.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.
  • 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?

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Variations

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