Abracadabra! Levitating with Eddy Currents!
AbstractDid you know that not all trains run on tracks? Some of the world's fastest trains are magnetic levitation trains (maglev). This means that the carriage of the train is suspended over the rails with no support, but only with magnetic fields! There is a physical explanation for magnetic levitation, and if you would like to learn more about magnetism and current, this is a science fair project that you must try!
Michelle Maranowski, PhD, Science Buddies
edited by Ben Finio, PhD, Science Buddies
This science fair project is based on the Eddy Currents snack on the Exploratorium's website:
Exploratorium. (n.d.). Eddy Currents. Retrieved December 12, 2008.
The objective of this science fair project is to demonstrate eddy currents and induced magnetic fields.
What is a magnet? A magnet is a material that produces a magnetic field, which can exert a force on other materials without actually touching them. A magnetic force can attract or repel, and some materials can exert a larger force than others. Every magnet has at least one north pole and one south pole. Did you know the Earth is a magnet? A magnet produces a field at all points around it in space, as shown in Figure 1. The Earth has a magnetic field that repels space radiation and solar wind. The magnet's poles (such as Earth's north and south poles) are where the magnetic field begins and ends. If you look at the magnetic field of Earth, you will notice that the magnetic field is not straight. The field starts at the north pole and bends as it meets the south pole. Since the magnetic field bends, it has a direction. You can read more about magnets and magnetic fields in the Science Buddies Electricity, Magnetism, & Electromagnetism Tutorial.
A large bar magnet overlays a drawing of Earth, the south side of the magnet points towards the north pole and the north side of the magnet towards the south pole. Magnetic field lines are drawn and have arrows that point in the direction the field is traveling. The magnetic field lines originate in the geographic south pole and travel around the Earth in large arcs returning to the geographic north pole.
Figure 1. This image depicts Earth's magnetic field.
Russian physicist Heinrich Lenz started studying electricity and magnetism in 1831. In 1834, while investigating magnetic induction, he noticed and described an interesting phenomenon. This phenomenon is now called Lenz's law and it occurs when a magnet interacts with a conductor. A conductor is a material that permits electrons (and therefore electricity) to flow through it easily. This means that a conductor has a low resistance and resistivity to the motion of electrons. When a magnetic field varies along the length of the conductor, like when you let go of a magnet down a metal tube, the magnetic field induces a current within the conductor. This current is called an eddy current. Once the eddy current is established, it then produces a magnetic field. This induced magnetic field opposes the magnetic field of the magnet that is moving along the conductor. As a result of two opposing magnetic fields, the magnet will stop moving and float, or levitate. This is the principle behind the world's fastest trains, called magnetic levitation (maglev) trains. There is no physical contact between the train carriages and the tracks.
Factors that increase the effect of eddy currents include stronger magnetic fields, faster-moving magnetic fields, and thicker conductors. Factors that reduce the effect of eddy currents include weaker magnets, slower-moving magnetic fields, and non-conductive materials.
In this project, you will investigate magnets and eddy currents. You will accomplish this by sending a neodymium magnet down a conductive tube and then down a non-conductive tube. Is there a difference between the ways the magnet falls down the two tubes? Do this science fair project and find out!
Terms and Concepts
- Magnetic field
- Lenz's law
- Eddy current
- What is a conductor?
- What is the difference between a conductor and a non-conductor?
- What is a magnetic field?
- Do you think a magnet will fall faster down a copper pipe or a PVC pipe?
- Davidson, M. (2006, June 15). Molecular Expressions: Electricity & Magnetism Introduction-Lenz's Law . Retrieved December 12, 2020.
This science fair project is based on the Eddy Currents project on the Exploratorium's website:
- Exploratorium. (n.d.). Eddy Currents. Retrieved December 12, 2008.
This HowStuffWorks video is a thorough discussion of Lenz's law and eddy currents:
- HowStuffWorks.com. Physics: Lenz's Law and Eddy Currents. Retrieved December 12, 2008.
There are several sources online that list resistivity values for different materials. The following are two examples.
Materials and Equipment
- Copper pipe, 1/2 inch inner diameter (at least 4 feet long), available at a hardware store
- PVC pipe, 1/2 inch inner diameter (at least 4 feet long), available at a hardware store
- 1/2 inch diameter neodymium magnet, available from from K&J Magnetics.
- Note: the magnet must have a smaller diameter than the inside diameter of your pipes. Since the inner diameter of 1/2 inch copper and PVC pipe is actually slightly more than 1/2 inches, a 1/2 inch diameter magnet should fit through the pipes.
- Lab notebook
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Neodymium magnets are very strong. Adult supervision is recommended when using them. Do not let the magnets slam together. They may pinch your fingers or crack. Keep them away from small children, pets, credit cards, and pacemakers.
- Create a data table like Table 1 to record the results of your experiment.
|Fall Time (seconds)|
|Type of pipe||Trial 1||Trial 2||Trial 3||Average|
- Hold the copper pipe vertically. Hold the pipe near the top with one hand, and have the volunteer hold the pipe near the bottom so it does not shake. Optionally, you can use something like duct tape or zip ties to fix the pipe in a vertical position (for example, by attaching it to the leg of a table).
- To do the experiment, you will need to drop the magnet down the pipe. You will need to start the stopwatch as soon as you let go of the magnet, and stop the stopwatch as soon as the magnet exits the bottom of the pipe. You and your volunteer should decide who will be in charge of the stopwatch.
- Hold the magnet just above the top of the tube, as shown in Figure 2.
Figure 2. Positioning the magnet for a drop.
- Release the magnet, and you (or your volunteer) should immediately start the stopwatch.
- Watch the bottom of the tube closely. You (or your volunteer) should stop the stopwatch as soon as the magnet comes out.
- Record the time in seconds under “Trial 1” for the copper pipe in Table 1.
- Repeat steps 4–7 for trials 2 and 3 with the copper pipe.
- Calculate an average value of your three trials for the copper pipe.
- Scientists do multiple trials and calculate an average to help even out any errors in their experiment. For example, in this experiment, there could be some human error in how fast you hit “start” and “stop” on the stopwatch.
- To calculate the average, add up the values, and divide by the number of trials (in this case, 3). For example, if your times were 4.5, 4.8, and 5.4 seconds, your average would be (4.5 + 4.8 + 5.4) ÷ 3 = 4.9 seconds.
- If you need help calculating an average, ask an adult for help.
- Repeat steps 4–9 for the PVC pipe.
- Make a graph of your results. Make a bar graph with the type of pipe (copper or PVC) on the horizontal, and the average fall time on the vertical axis. Try the Create a Graph website if you need help making a graph.
- Did the magnet fall down one pipe faster than the other? How can you explain your results?
Ask an Expert
- Repeat this experiment using tubes of different conductors. For example, try using a brass tube and an aluminum tube.
- What happens as you increase the diameter of the tube? Does the time it takes for the magnet to fall down the tube decrease, increase, or remain the same?
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