September 2017 Dancing Wire

Build a Electric Motor (Dancing Wire) (9/6/17)

MATERIALS:

  • AA Battery
  • Neodymium Button Magnet (Can be purchased online or at a few hardware stores)
  • Bare Copper Wire
  • Safety Gloves
  • Wire cutter
  • Pliers (only needed if your copper wire is too thick to bend by hand)
  • Adult Assistant

INSTRUCTIONS:

  1. Carefully place the neodymium magnet on the negative terminal (the flat side) of the AA battery. Neodymium magnets are extremely strong rare-earth magnets, and they could possibly pinch your finger tip between the battery and the magnet, so be VERY careful!
  2. Cut a piece of copper wire about 1 foot long (this does not have to be exact).
  3. *It is strongly recommended that you wear safety gloves when bending the wire! Once cut, the wire ends are usually very sharp!* Either by hand or using a pair of pliers, bend the wire to form a balanced motor apparatus. The photo to the right demonstrates one way to shape the wire into a symmetrical frame, but any shape that can balance from the positive terminal of the battery will work. The wire must also hang down so that it also makes contact with the battery.
  4. Place the neodymium magnet/battery apparatus on a flat surface. Carefully balance the copper wire on the positive end of the battery (it may be helpful to press an indentation into the terminal’s dimple, simply by pushing a pen tip into it.
  5. If you don’t see motion right away, then give the copper wire a gently tap to get it going. If the wire still is not moving, you may need to reshape the copper wire for a better connection. Remember, the wire must be able to balance on the positive terminal of the battery while also making contact with the battery below.

HOW DOES IT WORK:

A Homopolar Motor is an example of a very simple Electric Motor. Electric motors are machines that can use electrical energy to create mechanical energy (in other words, they create motion from electricity.) The rotational motion of a homopolar motor is caused by something called the Lorentz Force. This force cannot be directly seen, but its influence is very noticeable. The Lorentz Force has been described by the following:

A conductor with a current flowing through it, when placed in a magnetic field which is perpendicular to the current, feels a force in the direction perpendicular to both the magnetic field and the current.

Wow. That’s a pretty intense description, but it is saying that an electric current that is flowing through a wire at a right angle to a magnetic field force will actually be pushed in a direction that is at right angles to both the current and magnetic field. Are you as confused as I am?

The ‘Right-Hand-Rule’ of electricity and magnetism is a trick that might help us more easily explain how the Lorentz Force works. Use the diagram below to visualize the direction of the electrical current (blue arrows), and the magnetic field (red arrows), particularly at the section within the pink circle.

With your right hand, point your index finger in the direction of the flow of electric current (to the left). At the same time, point your right-hand middle finger in the direction of the magnetic field (down). Finally, stretch out your right-hand thumb as far as it can go. Your thumb (which should be pointing directly toward yourself) is now pointing in the direction of the Lorentz Force. Knowing this, we would expect the wire to spin counter-clockwise around the battery!

GOING ONE STEP FURTHER:

  1. If the neodymium magnet was flipped upside down, you would also flip the directions of the magnetic field forces. Would the copper wire spin in the same direction, or in the reverse direction, if you flipped the magnet? Use the Right Hand Rule to help develop a hypothesis.
  2. Instead of using the Lorentz Force to spin a wire around the magnet, could you find a way to spin the magnet itself? Actually, Yes! Try this follow-up experiment below.

Bonus Build: Lorentz Spinner

 MATERIALS:

  • D Battery
  • Electrical Tape
  • Copper wire (about 8 inches long)
  • Metal Screw
  • Neodymium Button Magnet
  • (Optional) Watch Battery and an LED light

INSTRUCTIONS:

  1. With a piece of insulating electrical tape, attach one end of the copper wire to the positive terminal of the D battery.
  2. Carefully place the neodymium magnet on the flat head of the metal screw. (Remember to be careful when using these strong magnets!)
  3. *Optional:* Using a small piece of electrical tape, attach the positive arm of an LED light (the longer wire) to the positive surface of a watch battery, as shown in the picture below. Test the setup by pinching the negative arm against the negative face of the battery and turning on the light.
  4. Lift and hold the D battery with the positive terminal pointing upward. Hang the tip of the metal screw (with the neodymium magnet attached) from the very center of the battery’s negative terminal. If the screw doesn’t magnetically stay attached to the magnet, you might need to add more magnets.
  5. If you are using an LED light, attach the negative face of the watch battery to the bottom of the neodymium magnet, ensuring that the un-taped wire is firmly pinched between the magnet and the battery. The light should turn on!Finally, touch the free end of the copper wire to the neodymium magnet. If nothing happens, try flipping the neodymium magnet(s) upside down and try again. In this experiment, the direction of the magnetic field force is very important!

May The Force be with you…the Lorentz Force, that is!!