In the teaching of science in lower secondary school (especially in Form Three), one of the topics taught is the formation of the magnetic field formed around permanent bar magnets. The conventional iron powder method currently used is decades old. In the old method, iron powder is sprinkled sparingly around an arrangement of magnet or magnets on cardboard. The cardboard is then gently tapped to set the iron powder in vibration and thus rearranges in accordance with the magnetic flux present.

Although this conventional method is simple and quite effective, the students always made a mess of the iron powder during every experiment. The iron powder always gets stuck to the magnets used, which is quite difficult to remove, except with the help of sticky tapes. Apart from this, the iron powder also drops on the table, which eventually has to be cleaned by the laboratory attendants. At times students over sprinkle the amount of iron powder thus resulting in unsatisfactory magnetic field patterns. There are even some students who purposely sprinkle the iron powder onto the magnets instead of around it, thus giving added cleaning job for the teachers and laboratory attendants.

I have been trying for years to design a method whereby the iron powder is totally separated from the magnets. After various trials with different ways, I have created my own magnetic field plate. It is very cost effective and user friendly. An added advantage is that it can even be used on an overhead projector. In the process of making the magnetic field plate, I have also designed a method of preserving the magnetic field patterns on metal plates and glass plates.

1. To provide a simple, clean and effective method of showing magnetic field patterns.
2. To give students an opportunity to make, preserve and keep the magnetic field patterns.

With the use of the magnetic field plate, there is no more contact of the iron powder with the magnets used. Thus the problem of iron powder sticking to the magnets is solved. There is no more spilling of iron powder on tables. The magnetic field plate is able to produce a perfect magnetic field pattern each time since there is always a uniform distribution of iron powder to form the magnetic filed. Even the slowest student is able to produce a perfect field (refer 1-P10a & 10b)

The experiment can also be performed as a demonstration through the use of the overhead projector, in situations when the class is too big or when there is not enough apparatus to go around. An added effect of this plate is that it is able to show and explain the fact that the magnetic field flux is under tension from the contraction of the flux as it is formed. The students are always fascinated when shown the magnified movement of the iron powder through the overhead projector (1-P11a, 11b, 11c & 11d).

The students' interest is greatly generated when they are taught the method of making the permanent magnetic field pattern using the waxes tin cover. They always show extra interest and are proud of things that they can make and take home. It costs almost nothing as it only uses tin covers, some candle wax and iron powder.

The merits of the magnetic field plate are that it always guarantees the formation of a perfect field pattern. On top of that it is very easy to use and very durable. The materials for making it is also easily available, at very lost cost.

The following are the materials used (refer 1-P1) :
Plastic sheets
Iron Powder
Liquid paraffin
Chloroform
MagnetsTin covers
Glass plates
Candles
Bunsen burner

1. Magnetic Field PlateThe magnetic field plate is formed by using 2 square plastic sheets (25cm ´ 25cm) sealed at he four sides by strips of plastic (1.0cm width) using chloroform (1-P2). Two tiny holes were then drilled at one of the sides of the plastic plate for filling purposes. The trapped air is then replaced by liquid paraffin mixed with iron powder through one of the tiny holes (1-P3). Once the plate is filled up to about 90%, the two holes are sealed off. The 10% trapped air is used for the purpose of redistribution of the iron powder each time a new magnetic field is to be studied.
2. Permanent Magnetic Field PatternsTo preserve the magnetic field pattern on tin covers (1-P4), a tin cover is first covered with a thin layer of melted candle wax (1-P5). The magnets are then arranged and stuck at the under side (uncoated) of the tin cover. Iron powder is then sprinkled sparingly on the waxed surface. The tin cover is the gently tapped to form the magnetic field pattern. The tin cover is then held over a burner with a small flame for about 5 seconds (1-P6). The powder is embedded in the melted wax and thus a permanent pattern is created.

The same method can be used to preserve the magnetic field pattern on a glass plate with added techniques (1-P7). The magnetic field pattern on the glass plate can also be shown on an overhead projector (1-P8).

The magnetic field plate (1-P9) is useful in the sense that it is very easy to use and it can be used to show magnetic filed patterns within seconds. To use the magnetic field plate, the plat is first shaken or inverted a few times to distribute the suspended iron powder evenly with the help of the trapped air bubble.

The plate can easily be made, as the materials required are easily available. The students can make it themselves and the project can be carried out as a society or club activity.

1. Magnetic field plate
   Liquid paraffin is not necessarily required to be introduced into the plate. Enough iron powder could be placed on the lower plate. Another plate is placed on the four plastic strips. The plates are stuck to the strips by using chloroform. Make sure that the space between the two plates is airtight. If possible it would be better to place some silica gel in the space between the plates before they are sealed.
2. Permanent magnetic field patterns
   Wax could be rubbed on a piece of aluminium or plastic sheet. A permanent magnet is placed on the sheet. Iron powder is sprayed around the permanent magnet and the sheet is knocked gently. Use candle flame to warm the wax on the sheet. The iron powder will stick to the wax when it cools.