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Measure Your Magnetism

Difficulty
Time Required Average (6-10 days)
Prerequisites Familiarity with using a solderless breadboard, or willingness to learn
Material Availability Specialty items are needed. See the Materials tab for details.
Cost Low ($20 - $50)
Safety Short circuits can get very hot. Double-check all of your wiring before you connect the 9 V battery.

Abstract

Do you know how to find the north and the south poles of a magnet? What materials are more magnetic than others? Is there a way to measure how strong a magnet is? Is there a way to measure the strength of an electromagnet? How much does the material that is in the core of the electromagnet affect its magnetic strength? With this project, you'll be able to answer these questions and many others. You will learn how to build and use a simple meter for measuring magnetic field intensity.

Objective

The goal of this project is to build a sensor for measuring magnetic field strength and to use it for measuring the strength of different types of magnets.

Credits

By Akram Salman  AMD logo

Edited by Andrew Olson, Ph.D., and Ben Finio, Ph.D., Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Measure Your Magnetism" Science Buddies. Science Buddies, 15 June 2015. Web. 1 Aug. 2015 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p030.shtml>

APA Style

Science Buddies Staff. (2015, June 15). Measure Your Magnetism. Retrieved August 1, 2015 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p030.shtml

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Last edit date: 2015-06-15

Introduction

Magnets and magnetic fields are used in everyday electrical equipment such as motors and refrigerators. You will also find them in electronic equipment like cell phones and radios. A magnetic field can be produced by a permanent magnet, or by electrical current flowing through a wire. You can make an electromagnet by wrapping a coil of wire around a magnetic material (e.g., iron, magnesium, or cobalt). When current flows through the coil, a magnetic field is produced.

Magnetic fields are also important in communication systems. The waves used to transfer information for television and radio broadcasts or cell phone calls are electromagnetic waves. Light, x-rays, and radio waves are all examples of electromagnetic waves.

A magnetic field can be visualized as magnetic filed lines. The strength of a magnetic field is defined as the density of magnetic field lines and is strongest close to the magnet. The strength of the magnetic field diminishes (lessens) with increasing distance from the magnet. Magnetic field strength is measured in units of gauss (abbreviated G). The device that is used to measure the magnetic field strength is called a gaussmeter.

The gaussmeter that you will build for this project is based on the Hall effect, discovered by Dr. Edwin Hall in 1879. Hall discovered that when a current is passing through a thin sheet and a magnetic field is applied perpendicular to the sheet, a voltage (called the Hall voltage) is generated across the third dimension, perpendicular to the direction of the original current. The magnitude of the Hall voltage is proportional to magnetic field strength. The Hall effect is used in different applications including making an electric motor.

Your gaussmeter will be based on an integrated circuit that allows you to measure the Hall voltage generated by a magnetic field. You'll learn how to build the gaussmeter, and how to use it to measure magnetic field strength. You'll also learn how to use your gaussmeter to identify the north and south poles of a magnet.

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:

  • Magnetic field
  • Electrical current
  • Electric voltage
  • Electromagnet
  • Electromagnetic waves
  • Magnetic field strength
  • Gauss
  • Gaussmeter
  • Hall effect
  • Multimeter

Bibliography

For learning about magnetism and magnetic fields, see this Science Buddies tutorial:

For learning about the Hall effect, this website is a good start:

To learn about the Hall effect sensor used in this project, see the product's datasheet:

This Science Buddies project has information on making your own electromagnets:

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Materials and Equipment

To do this experiment you will need the following materials and equipment, available from Jameco Electronics:

If you want to build and measure the strength of simple electromagnets, instead of permanent magnets, you can use the Science Buddies Strength of an Electromagnet Kit, available in the Science Buddies Store.

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Experimental Procedure

Note Before Beginning: This science fair project requires you to hook up one or more devices in an electrical circuit. Basic help can be found in the Electronics Primer. However, if you do not have experience in putting together electrical circuits you may find it helpful to have someone who can answer questions and help you troubleshoot if your project is not working. A science teacher or parent may be a good resource. If you need to find another mentor, try asking a local electrician, electrical engineer, or person whose hobbies involve building things like model airplanes, trains, or cars. You may also need to work your way up to this project by starting with an electronics project that has a lower level of difficulty.

The Experimental Procedure for this project has four sections, which are described briefly below.

  1. Building the Gaussmeter. This section has the step-by-step instructions for assembling the gaussmeter circuit.
  2. Measuring Magnetic Fields. This section shows you how to use the gaussmeter to measure magnetic fields.
  3. Analyzing Your Results. This section shows you how to calculate magnetic field strength from your measurements, and also how to identify the north and south poles of a magnet.

Building the Gaussmeter

To build the gaussmeter, you will need a voltage regulator integrated circuit (IC) and a Hall Effect linear IC. The purpose of the voltage regulator is to convert the 9 volts from the battery into a stable and constant 5 volts that the Hall Effect IC needs to function. The Hall Effect IC is a ratiometric or linear device, which means that the output is directly proportional to the input.

  1. Assemble the circuit on the breadboard as shown in Figure 1. If you do not know how to use a solderless breadboard, see the Science Buddies project Electronics Primer: Use a Breadboard to Build and Test a Simple Circuit.
    1. Orient the voltage regulator so the writing on its front side is facing to your left. Insert the 3 pins of the voltage regulator into holes E2, E3, and E4.
    2. Orient the Hall effect sensor so the writing on its front side is facing to your left (look closely, the writing is tiny!). Spread the three pins apart slightly so they will fit into three adjacent breadboard holes. Connect them to holes E7, E8, and E9.
    3. Use a short jumper wire to connect hole A2 to the positive power bus (note: although red is traditionally used to represent positive in circuits, you do not have to use a red wire. This applies to all the other wires in the circuit as well - your wires do not need to match the colors in the diagram).
    4. Use a short jumper wire to connect hole A3 to the ground bus.
    5. Use a short jumper wire to connect hole A8 to the ground bus.
    6. Use a short jumper wire to connect holes C4 and C7.
    7. Connect a long jumper wire to the ground bus, and leave the other end unconnected (later you will connect it to your multimeter).
    8. Connect a long jumper wire to hole C9, and leave the other end unconnected (later you will connect it to your multimeter).
    9. Connect the red wire from the battery holder to the power bus (do not insert the battery until you have double-checked all your wiring!).
    10. Connect the black wire from the battery holder to the ground bus.
    11. Your completed circuit should look like the one in Figure 2 (remember that your wire colors do not have to match).
    12. Important: double-check all your connections before you snap the battery into the battery holder. If you connect something incorrectly and create a short circuit, the circuit parts can get very hot.
gaussmeter breadboard diagram
Figure 1. Breadboard diagram of the gaussmeter circuit.


photo of gaussmeter circuit
Figure 2. Example photo of the gaussmeter circuit on a solderless breadboard.
  1. Now, use alligator clips to connect your multimeter's probes to the long wires from your breadboard, as shown in Figure 3.
    1. Connect the red probe (which should be plugged into the port labeled VΩMA) to the jumper wire in hole C9.
    2. Connect the black probe (which should be plugged into the port labeled COM) to the jumper wire in the ground bus.
    3. Set your multimeter to measure DC volts. If you do not know how to use a multimeter, see the Science Buddies Multimeter Tutorial.
gaussmeter and multimeter
Figure 3. Multimeter connected to the gaussmeter circuit with alligator clips.

Measuring Magnetic Fields

Follow these steps to use the gaussmeter to measure the electric field:

  1. Observe the value read by the multimeter. With no magnet near the sensor, you should see a reading of approximately 2.5 V (it may be a little higher). This value is considered the zero level of the gaussmeter. We will call this level V0.
  2. To measure the strength of a magnet, touch it to the front of the Hall sensor, as shown in Figure 4. (The front side of the IC has the brand name on it and angled sides. The Hall sensor element is right in the center of the chip.) Experiment with different orientations of the magnet to see where you get the maximal response.
  3. If the Hall voltage decreases, you are measuring the north pole of the magnetic field; if the Hall voltage increases, you are measuring the south pole.
  4. Observe the new voltage on the multimeter and record it in your lab notebook. We will call this level V1.
  5. Repeat steps 1–3 for each magnet you want to test.
  6. Check your understanding of how the Hall-effect sensor works by answering the following questions:
    1. What happens to the readout voltage if you touch the same side of the magnet to the back side of the Hall sensor IC?
    2. Why?
gaussmeter science project
Figure 4. Test the gaussmeter by touching a magnet to the front side of the Hall sensor, as shown.

Analyzing Your Results

  1. The sensitivity of the Hall sensor IC described in this experiment is 1.3 mV/G (see the product's datasheet). Therefore, to calculate the magnetic field strength, B, in gauss, you can use this equation:
    B = 1000 × (V0 − V1) / 1.3.

    Your measurements, V0 and V1, are in volts. The factor of 1000 converts your measurement to millivolts, in which the Hall sensor is calibrated.
  2. Use the equation to calculate the magnetic field strength for each magnet. (If you are using a different Hall sensor IC, substitute its sensitivity in the equation above.)
  3. Check your understanding of the field strength calculation by answering the following questions:
    1. The Hall sensor IC used in this project is supposed to have a linear response throughout the supply voltage range (0–5 V). Assuming a V0 of exactly 2.5 V, what is the maximum magnetic field strength that can be measured with this device?
    2. Is the value the same for both north- and south-pole magnetic fields?

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Variations

  • An interesting variation is to use your gaussmeter to measure the strength of electromagnets with different number of turns. Here are the steps (see the Science Buddies project The Strength of an Electromagnet for more details):
    • Create several electromagnets with different number of turns (e.g., 50, 100, 150, 200).
    • Allow current to pass through the electromagnet. Use the same battery for each electromagnet.
    • Measure the magnetic field for each electromagnet using steps 1–3 from the previous section. Try to power the electromagnets as briefly as possible, since they tend to drain the battery quickly.
    • On graph paper (or using a computer graphing program), plot the value of the magnetic field strength on the y-axis versus the number of turns used for the electromagnet on the x-axis.
    • What is the relationship between number of turns and magnetic field strength?
  • The core material of the electromagnet also affects its strength, so another interesting experiment would be to vary the core of the electromagnet and see how much it affects the measured magnetic field. For example, you could use more nails, you could try steel bolts, you could try different shapes.
  • Another idea would be to map the magnetic field distribution around the magnet. You would need to measure the magnetic field strength at many points around the magnet, and then use the data to draw a map of the field strength. One way to do this would be to pick several constant values of field strength, then vary the distance of the magnet from the sensor until the multimeter reading matches that value. Record the distance and orientation of the magnet for each measurement. This way you will be measuring the points at which the magnetic field strength is equal, making it easier to draw a contour-line map.

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