Build a Electromagnet

Electromagnets are a type of magnet which the magnetic field is produced by an electric current. It consists of a wire wound into a coil that has electricity passing through it. A coil that is wrapped into the shape of a cylinder is called a solenoid. When current is introduced, either from a battery or another source of electricity, a magnetic field is created around the coiled wire which causes it to magnetize.

Electromagnets are different from “permanent” magnets (which have two poles: north and south) because the magnetic field only exists when electric current flows through it. If you stop the electric current, then the coils do not act like a magnet anymore.

Electromagnets often have a piece of iron or ferromagnetic material in the middle of the coiled wire to increase its strength. Ferromagnetic materials contain tiny areas called magnetic domains which are regions in which the magnetization is in a uniform direction. These magnetic domains, which act like small magnets, line up with the magnetic fields made by the solenoid thus increasing the overall strength of the electromagnet.

In healthcare, electromagnets are used in Magnetic Resonance Imaging (MRI) machines to produce detailed imaging of the human body, helping doctors diagnose and treat various conditions. MRI machines use magnetism and the large percentage of water in the human body to create detailed, high contrast images of the human body.

When taking an MRI, patients are placed on a table in the center of a cylinder surrounded by electromagents, permanent magnets and coils of wire. The water molecules (specifically the hydrogen atoms) inside the body are magnetized in the same direction by a large magnetic field. Since different types of body tissue respond to different frequencies, a radio frequency pulse is directed at the body structure being examined which energizes the hydrogen atoms of a specific tissue and causes them to flip out of alignment from the rest of the hydrogen atoms in the body. When the radio frequency is removed, the flipped hydrogen atoms slowly return to the magnetized state and release the energy received from the radio frequency. The coils of wire in the machine detect the energy that is released and an image is captured! This is why MRI machines are often used to image non-bony parts or soft tissues of the body because they contain more water (ie: hydrogen atoms), thus producing a better image.

Did you know?

• The main magnet in a MRI's magnetic field is 140,000 times stronger than Earth's magnetic field.

• MRI machines do not emit radiation making them safer for patients.

Materials included in kit:

• Safety Googles

• AA Battery + Holder

• 9V Battery + Holder

• Iron Nails

• Alligator Clips

• Copper Wire

• Paper Clips

Build Instructions:

Build instructions provided by ScienceBuddies

1. Make two different electromagnets—with 50 and 200 turns of wire, respectively—by tightly winding the magnet wire around the iron nails. See Figure 1.

2. Make a data table, like Figure 2, in your lab notebook.

3. Place the paper clips in a pile on a flat surface.

4. Starting with the 50-turn coil, use the electromagnets to pick up paper clips from the shallow container.

   • Important: Your electromagnets will get hot if you leave them connected to the battery in between tests. Always disconnect one alligator clip when your electromagnets are not in use.

   • Connect one end of the red alligator clip to the "+" terminal of the AA battery, and the other end to one end of the wire coil. Make sure you connect to the part where you sanded off the insulation.

   • Connect one end of the black alligator clip to the "-" terminal of the AA battery, and the other end to the free end of the wire coil. As soon as you do this, your electromagnet will turn on and begin to heat up, so it is important to work quickly.

   • Touch the head of the nail to the pile of paper clips (Figure 3), and then pull the coil away from the paper clips (Figure 4). There should be some paper clips attached to the nail.

     • If it does not lift any paper clips at all, then your electromagnet is not working. Check that the electromagnet is correctly connected to the battery. Make sure the alligator clips are connected to both the battery and the wire. If the clip leads are connected correctly to the coil and battery, but the electromagnet is still not working, then the problem may be that the magnet wire is not completely stripped and try re-sanding the ends of the copper wire to remove the insulation.

   • Move the nail away from the pipe of paperclips (Figure 5), and then disconnect one alligator clip (it does not matter which one, and you do not need to disconnect all four alligator clips). This should turn your electromagnet off and the paper clips should fall away from the nail.

   • Count the number of paper clips that the magnet picked up, and record this value in your data table.

   • Return all of the paper clips to the container.

5. Repeat step 4 four more times, for a total of five trials.

6. Repeat steps 4-5 for the 200-turn coil. Always remember to disconnect your electromagnets from the battery when not in use.

7. Analyze your data.

   • Calculate the average number of paper clips picked up for each number of turns in the coil.

   • Does the number of paper clips picked up increase or decrease as you increase the number of turns in the electromagnet?

   • Try experimenting with the 9V battery size. How did your results differ?

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