Aim

In 1820, Professor Oersted (Denmark) accidentally found out the relationship between electric current and magnetic field, which led to the great discoveries of the electromagnet, motor and generator. This important experiment is inadequately taught in classes today. The conventional experiment apparatus used may be categorized into two types as shown in diagrams 8-1D & 2D, both of which are demonstration experiments using OHP. It is difficult to understand the three-dimensional magnetic field with a two-dimensional image of the OHP and, as a matter of course, it is not easy for students to deepen their interest in electromagnetism.

Diagram 8-1D

Confirm magnetic field with a magnet or iron dust made by passing 30A of high-capacity electric current through an electric cord. In order to do this, it is necessary to get hold of a special low-voltage high-capacity electric power source, which is not readily purchased nor easily made, so it is not feasible for letting each student do this experiment.

Diagram 8-2D

Pass a few amperes of electric current through a coil made by winding enameled wire 30 to 40 times. As a whole, it would be the same as passing high-capacity electric current and we may conduct the same experiment as with Diagram 8-1D. This is the more popular method but is still not commonly done by individual students. The reason is presumably in the coil itself.

There is a method for individual experiment by using electric current made when short-circuiting a battery with a short electric wire. However, the magnetic field made in this way is insufficient and the experiment will be unclear and too short. Also, even with a battery, short-circuiting for the sake of experiment is not desirable.

I would like to introduce my invention of a simple method of getting a stable "high-capacity electric current" which would be useful for students to easily understand the relationship between electric current and magnetic field.

Outline

I got the hint for my invention from the cord made up of thin electric wires of different colours inside the intercom. It struck me that if I solder the wires so that they are connected in a series, it will become a giant coil passing a flow of high-capacity electric current with just a little current. This is in principle the same as the experiment apparatus of Diagram 8-2D, but when made long and large enough, it may be considered as one electric cord instead of a coil.

This is the key point though it is not the truth. When I showed the interior structure of the apparatus to the students at the end of the class, I was greatly encouraged by the fact that they could understand the principle quite easily and helped them become interested in electromagnetism. Afterall, any circuit is in fact one loop of big coil. Diagram 8-3D shows a connecting method of the "high-capacity electric cord" using a 2-wired cable. Actually, we used a 10-wired cable.

Recently, electromagnetic induction experiment made by passing through an electric cord a flow of alternating audio electric current instead of direct current is being conducted. This experiment is not only possible with the "high-capacity electric cord", but is very convenient for classes as it is easily made into a coil.

Method of Making Teaching Material

1. Characteristics of Apparatus

For practical use, I used "MVVC10 wire x 0.3mm2" conducting cord made by covering with sheath 10 different-coloured vinyl electric cords. Each vinyl electric cord is made up of a bundle of thin copper wires so, unlike the single-wired intercom cable, it is flexible and easy to handle. "High-capacity electric cord" made of 6m of such conducting cord consists of 10 loops of cord connected in a series, which will be equal to 60m of electric cord, with a total electric resistance of a surprising 3.5a. So if we want a current of 4A, we would only need 14V of electric supply, which would be of no problem with an ordinary laboratory power source (usually 0 to 15V/5A).

As the result, as there are 10 loops of the cord, we would get a very strong magnetic field of an electric current equal to 40A. 6m would be just right to circle a laboratory table where about 10 students may participate in the same experiment. To use a longer cord, we may connect two or more apparatus in series and increase the voltage. The temperature of the cord will rise a little but is of no problem, and will be quite useful as proof that a current is flowing.

Moreover, the rise in temperature makes the cord more flexible and easier to handle. If we fit it with a power switch and a polar transition switch, all sorts of classes may be conducted. This apparatus is not only cheap, just one apparatus will be enough for all the students to conduct experiments.

2. "High-Capacity Electric Cord" - (Photo 8-1P)

3. Close-Up of Circuit Connection - (Diagram 8-4D)

4. Necessary Articles

• Vinyl electric cord: MVVC10 wire x 0.3mm2 (necessary length). Note : Thickness and quality may vary according to manufacturer.
• Switch : 2-circuit 2-connection middle OFF slide switch.
• Connector : 10 pins (e.g. Satoh Parts CN-35).
• Terminals : red, black.
• Acrylic sheet (or aluminum sheet for fitting parts) : 26 x 180mm (black, 3.0mm thick).
• Lauan plywood (for lid and bottom and for spacing in between) : 120 x 180mm (2 x 5.5 mm thick; 1 x 15 mm thick).

Guidance Method

1. Electric Current and Magnetic Field

Pass 3 to 4A of direct current through the "high-capacity electric cord". Students encircling the cord with compasses or iron dust in hand may observe the movement of the compass and patterns of iron dust. Reverse the flow of current and the direction of the compass will change so the relation between electric current and magnetic field can easily be understood. Make a loop with the cord and many magnetic field will be bound together, which will help students understand easily the value of the coil. Make more loops and the magnetic field will strengthen. As experiment with this apparatus can be done in a group, the students can discuss with each other so that they may deepen their understanding.

2. Electromagnetism

A "high-capacity electric cord" passing a flow of 3 to 4A of direct current sound round an iron bar several times will become an electromagnet attracting such things as staples. As we can see clearly how the coil is wound, we may have the students predict the relation between the direction of current and the magnetic poles and afterwards prove it by experiment. The magnetic field may also be confirmed by magnet. This experiment is exactly the same as the diagrams shown in textbooks and exercise books but so far it has been difficult to conduct experiments with the same number of loops because the current was not enough. (Photo 8-5P).

3. Electric Swing

Pass a bar through an experiment stand and hang a "high-capacity electric cord" in a U shape. Place a horseshoe magnet between the bottom of the cord and pass 3 to 4A of direct current and we will get an electric swing. (Photo 8-6P)

In the past, this experiment was done in a rather complicated fashion, like in diagram 8-5D using a coil, or diagram 8-6D devising a movable mechanism, or like in diagram 8-7D using aluminum foil or other materials. All this was on account or not being able to get high-capacity electric current, but with this cord we can make a simple electric swing.

Also, if we hang two sets of these cords facing each other, we may observe the influence of parallel current. However, it is rather tricky to set the cords so that they are parallel.

4. Geomagnetic Generator

If two people hold a "high-capacity electric cord" and swing it up and down, the influence of the magnetic field of the earth will make this a generator, passing a few hundred 4A of electric current. We may try swinging it in different ways or changing the direction.

5. Electromagnetic Induction

Pass a sound signal of an output of a few W through a "high-capacity electric cord", receive it with a coil made by winding enameled wire 50 times, and we can hear music from earphones or a speaker connected to it.

With this experiment, we may confirm from the direction of the coil and distance from the cord the direction and density of the lines of magnetic force. If we make a loop (coil) with the cord and bring it close to the coil with a speaker connected to it, the sound will increase. Increase the number of loops or pass an iron bar through it and the sound will become louder and will reverberate throughout the classroom. Just by bringing close an empty can with a magnet stuck to it or a piece of paper sound is produced, so we can say that it is the ultimate simple speaker.

This sound receiving experiment using electromagnetic induction has been conducted in some parts by making a giant coil by bundling electric wires. However, with this method, the coil cannot be said otherwise, so that there is a limit to experimenting in this way. On the other hand, the "high-capacity electric cord" is enclosed into one cord and can easily be made into a coil, and along with the experiment done with direct current there is potential to develop the experiment into all sorts of directions. I might add that this principle is nothing new, but is already in practical use under the floors of room for people with hearing disorder (received with hearing aid) and for guide in art museums (received through an exclusive receiving device).

Also, a 100V electric wire, the voltage lowered to 30 to 40V with a transformer, may be used in all sorts of experiments.

Effectiveness Upon Practical Use

When actually used, this cord helped students to behave independently by "each student manipulating in their own hands the magnetic fields and thinking things out". The apparatus may intentionally be manipulated by the teacher as well and made to follow the experiment. This method is unique in that it may be classified as individual experiment, demonstration experiment as well as group experiment. The uniqueness of this method can be understood by anyone doing these experiment. It helped to understand the experiments much better than with the conventional methods. The merit of the "high-capacity electric cord" is that it helps recognize the importance of the teacher while at the same time easing the burden.

Note :
This method was invented 13 years ago, and since it is being used widely mainly in schools of Kyoto City, the apparatus has been improved and new methods of its use discovered. The result is that it can be used for so many varieties from experiments the name has become inappropriate. Therefore, taking the name from the research group that took the lead to promote the method [Pascal Kyoto], we are in the process of spreading the use of this apparatus under the name [Pascal Electric Cord].