Background:

Tom Hawkins: I am a elementary school teacher from Palm Beach County Florida. I currently teach at S.D. Spady Elementary Montessori Magnet School. My students range in age from 6 to 9 years old...that would translate into 1st through 3rd grade. Our Montessori classrooms are multiage and I will usually teach a child for three years.

RET is a program sponsored by The National Science Foundation, where teachers work with scientists like Donavan Hall to better understand what research scientists do while at work. The experience is then translated to the students in the teacher's class. There are two goals of the program: one is to excite both teachers and learners about the possible career opportunities in the field of science, and the other is to take a project back to the classroom that the teacher creates with the help of the mentor scientist. A description of my project follows.

The Project: To build an impulse magnet
What is an impulse magnet? In this case it is a coil of wire that is non-magnetic when it is not charged, but when an electrical charge is sent through it, it creates a magnetic field. The electrical charge is "pulsed" or sent through the coil for a very short time via a capacitor bank. The object of making my pulse magnet is to launch an aluminum ring that sits on the coil. I believe that this demonstration will produce a great deal of excitement among my studenets and, with other activities, will demonstrate important principles such as circuitry, magnetism, and the movement of electrons.

Pictured below is the initial circuit. As the process began I originally made the circuit on a bread board to assure that, if there were problems, I would be able to reconfigure the circuitry. As the process continued, it became evident that this was a very important step. The original idea was to build an impulse magnet that children would be able to use safely. After some initial calculations it was determined that a 12 volt power supply would be sufficient to power the magnet.

Once the circuit was completed on the bread board it was time to test my electronic handywork. After a few revisions (yes, I connected things in the wrong order) the circuit was complete and operated as designed. It was very helpful of the Magnet Lab to provide me with electrical engineering help from Andy Powell and a complete electronics lab in which to work!

Below is a picture of the first capacitor bank with the impulse switch. The green lead would light when the capacitors were charging and the red lead would light when the capacitor bank was charged.

 

Pictured below is another version of the circuit board. The original design had a fire button, toggle switch for charging and a three-way switch to change the voltage going to the coil. All of it functioned properly but the voltage created was not enough to create a strong enough field in the coil to move even a 3g washer. It was time to rethink the design and parameters of the project. After some discussion with Andy, the Electrical Engineer, it was decided that we would test this circuit at several different voltages. Again, it's great to have a well supplied shop at your disposal.

 

In this photo we used an adjustable power supply and tested the circuit up to 200 volts. At 200 volts we generated a powerful enough field to launch a 3.5 gram ring 20 feet. After this test we decided to build a new circuit at 200 volts without the variable switch. I believed that I could change the mass of the object being launched instead of the voltage. This would make a more durable circuit and still give me an adjustable parameter.

 

This is the new design. Notice that there are only 5 capacitors.
In this configuration the circuit develops 2800 micro farads at 175 watts. This combination develops approximately 42 joules.
2800E-6/2X(175)²
 This energy is equal to what it would take to light a 40 watt light bulb for 1 second.

Below is the finished product with the coil.

This is a photo of the different types of coils that I tried before settling on the pancake coil that I use during demonstrations.