How We Built and Tested Our Electromagnet

We made our electromagnet with a steel bolt and 20 gauge plastic insulated wire.

	We held one end of the wire against the bolt, with a few centimeters hanging off to the side. The next step was to wind the wire onto the bolt in layers, going back and forth until the 250cm length was mostly used up, except for a few centimeters.
	We twisted the two free ends together. Using a wire stripper, we removed about 2cm of insulation from each end of the wire. A knife will do in place of the wire stripper. We could have used enamel-coated wire instead. The enamel is a kind of paint that insulates the wire in the same way as the plastic. The enamel can be removed from the ends of the wire with sandpaper.
	To use the electromagnet we held the ends of the coil of wire against the battery and lifted some paper clips. This electromagnet lifted 21 paper clips. These were the same paperclips that we used for the Clay Boat challenge.
	We weighed them then and determined that on average, each one weighed 0.52 grams. So, our electromagnet lifted 10.92g - not very impressive. No doubt you can do better.

Tips

There are many factors that affect the strength of an electromagnet. Here are some things to consider as you design and build yours:

• The more turns of wire, the stronger the magnetic field.
  You are limited to 250cm of wire. You should probably use all of it. The number of turns you can get out of a given length of wire is affected by how you wind it. Neatness counts.
  
• The larger the diameter of the coil, the stronger the magnetic field.
  But, since you are limited to a fixed length of wire, increasing the diameter of the coil will mean fewer turns.
  
• The length of the coil affects the strength of the electromagnet.
  If the length of the coil is equal to the radius, then increasing it further will reduce the strength of the electromagnet. The relationship between radius and length gets complicated. SEED Expert Ramon Hernandez gives this explanation of how radius and length of an electromagnet coil affect its strength.
  
• The more current the electromagnet draws, the stronger the magnetic field.
  Since we have fixed the voltage at 1.5v, the resistance of the coil determines the amount of current it will draw. According to Ohm’s Law:I = V / R
  where I is current, V is voltage and R is resistance. The thinner the wire, the higher its resistance.
  
  
• The amount of current that the electromagnet draws may actually be less than what is determined by Ohm’s Law.
  The additional limitation is the power source, which has a maximum current that it can deliver. Not all 1.5v volt batteries are the same in this regard. A size D battery has a greater capacity than an AAA battery. Also, there are many different battery types of the same size. We used an alkaline battery. There are also inexpensive carbon and zinc batteries and a variety of rechargeable types including Nickel-Cadmium. Finally, a fresh battery has a higher capacity than one that has been used for a while.