Teaching Magnetism with Home-Made Experiments

Physics Education • January − March 2007 243

Teaching Magnetism with Home-Made Experiments

SOMNATH DATTA 656, ”Snehalata”, 13th Main, 4th Stage, T K Layout, Mysore 570009, India

Email: [email protected] Website “Physics for Pleasure” :http:// www.geocities.com/somdatta_2k

ABSTRACT

The article presents a methodology for teaching the basics of magnetism in which concept-centred experiments (CCEs) made in a home workshop form an integral part. The author has first presented a brief review of the basic principles of magnetism followed by the CCEs that may facilitate this learning process. He has mentioned four experiments, one of which had been published earlier. After a cursory reference to that experiment the author has presented details of the other three experiments, the concepts they illuminate, and the data obtained from these experiments.

1 Introduction

Over the last two decades we have been contributing low-cost concept-forming physics experiments in the areas of mechanics and electromagnetism, most of which had been published in this journal. A round-up of these experiments was also published in this journal under the title “Concept-Centred Experiments in Physics” (CCEs).1 The present article is a continuation of that dialogue.

In this article we would like to present a

combination of CCEs and theory that a teacher at the +2 or college level may find useful in his classroom teaching of the fundamentals of magnetism. The experiments are “home-made”, a phrase we would like to stress to highlight our belief that experiments that can hold students in absorbing attention and at the same time convey a lot of “physics with conviction”, can be made in as little a space as a garage, by a teacher himself, using some basic tools and at a very small expenditure. The reason we have chosen magnetism is that since

244 Physics Education • January − March 2007

publication of the earlier article we have designed a set of three new experiments intended to facilitate understanding of this particular topic.

There is this need for devising simple low-cost experiments which will fulfil a particular objective of a teacher who is struggling to convey the full meaning of a concept or an equation to his young audience. The CCEs we devised over a span of time were born out of such needs felt in the classroom. Therefore

these experiments should not be seen in isolation, but as part of a set of lessons. In this article we shall discuss our experiments in juxtaposition with the concepts and principles (i.e., the theory) they will illuminate.

2 The Fundamentals

We shall review what we consider to be the fundamentals in the theory of magnetism.

Figure 1. Explaining: Biot-Savart’s Law in (a) and (b); Ampere’s Law in (c).

Fundamental 1. Magnetism originates due to the flow of electric currents, which can be externally manifest (i.e., measurable with a meter) as in conduction currents flowing in a metallic wire, or can be internal currents, effectively due to the orientation of the spin and orbital angular momenta of the atomic electrons, as in the case of magnetized materials. Fundamental 2. The magnetic force is a velocity-dependent transverse force. By this we mean that an electrically charged particle carrying charge q and placed in a magnetic field B will experience a magnetic force Fm only when it is in motion, and that this force will be perpendicular to the direction of its velocity v. This force is given by the Lorentz force equation:

Fm = qv × B. (1)

Corollary 2A: If we place the straight segment of a conductor carrying current I in a “uniform” magnetic field B produced in the region between the pole pieces of two magnets (such that the N-pole of one faces the S-pole of the other with a gap in between), then the conductor experiences the force

Fm = I(L × B), (2)

where L is the “length vector” of this segment lying within the pole pieces of the magnets, its magnitude being L and its direction being the direction of the current.

From this point onward we shall restrict ourselves to static magnetism. A static magnetic field can be produced by a constant electric current flowing through a closed coil.


Fundamental 3. The time-independent magnetic field B(r) produced at a point r is given by Biot-Savart’s law which can be expressed in either of the following two forms

B r s r rr r

B r J r r rr r

( ) ( )| |

. ( )

( ) ( )| |

. ( )

=′ × − ′

− ′

=′ × − ′

− ′′

∫∫∫∫

μπ

μπ

0

0 3

4

4

I d a

d r b

C

V

3

3( ) (3)

In the above I represents a steady current flowing through a closed conducting wire C, ds′ is a directed line segment of C at r′ (Figure 1a), J(r′) is steady current density at r′ (Figure 1b), d3r′ is a volume element at r′. The

constant μ0 is called permeability of free space, whose value can be expressed in the convenient form:

0

4μ

π = 10–7 T.m/A (4)

At this point, and for subsequent discourse on electromagnetism it is essential that the teacher introduces the concept of an oriented surface and its directed boundary, without which it is impossible to teach the basics of electrodynamics, in particular, Ampere’s law and Faraday’s law of electromagnetic induction.

Figure 2. Application of Ampere’s Law for computing B (a) near a long straight current carrying conductor, (b) inside a long solenoid of arbitrary cross section.

Definition of the Directed Boundary of an Oriented Surface

S is an oriented (in general, curved) surface as shown in Figure 1c. By this we mean that it has a definite positive side and a definite negative side. (The teacher should recognize that there are non-orientable surfaces.3) We have indicated the positive side of S with the + sign. This surface S is not closed, so that it has a

“boundary” Γ which is a closed curve. We assign Γ a positive direction (indicated with an arrow) which is taken to be anti-clockwise when looked at from the positive side of the surface.

This strange “asymmetric” direction relationship can be traced to the right-hand-rule (RHR) associated with vector “cross product”. The statement in the above paragraph, translated into RHR would be read


as follows. If the thumb of the right hand points in the direction of the positive direction of the surface, then the other fingers would be seen curling in the positive direction of the boundary curve.

We now come to Ampere’s Law which can be derived from Eq. (3b).

Corollary 3A: Ampere’s Law. Let there be steady currents I1, I2, such that the net current crossing S from the negative side to the positive side is ΣI. Then this distribution of currents creates a B field whose line integral around the closed path Γ, taken in the positive direction, is given by Ampere’s Circuital formula:

0.d IΓ

=μ ∑∫ B r . (5)

For the example depicted in Figure 1b, ΣI = I2 – I3 + I4.

Evaluation of B by performing the line integral (5) is often difficult. In certain instances of direct concern to us, however, we come across distributions of electric current which present a kind of “symmetry”. Simultaneous application of Ampere’s law and the symmetry consideration can lead to a simplified, even if approximate, computation of the B field. Two instances of such computation have a bearing on two of the experiments that will follow.

The first example is the magnetic field in the vicinity of a long straight segment AB of a closed coil ABCD (Figure 2a) carrying electric current I. It is assumed that the adjacent sides BC and DA are perpendicular to AB and long, so that the segments BC, CD and DA make little contribution to the field at a point P near the centre of AB. Let r be the distance of P from AB and L be the length of AB. It is assumed that r L. Then “by symmetry” the magnetic field lines make coaxial circles around the straight wire. A path C that passes through P and also coincides with a field line

has a path length L = 2πr, and the current crossing the surface is I. Hence from Eq. (5)

BIr

≈μ

π0

2. (6)

The direction of this B field is given by the curling fingers of the right hand with the thumb pointing in the direction of the current I.

The second example is of a long solenoid (of arbitrary cross-section) whose lateral dimension b is very small compared with its length L (Figure 2b). This solenoid is carrying a current I which flows through N turns. The field inside the solenoid is strong and nearly parallel to its axis, having an average value Bin. The contribution from that part of the path C which lies just outside the solenoid is rather small. The left side of (5) is approximately BinL whereas the right side is μ0IN. Hence,

BINLin ≈

μ0 (7)

The direction of the B field is such that if the right hand thumb aligns along it, the other fingers would be curling in the direction of the current I.

We shall now note here one important aspect of current-current interaction that follows by combining Eq. (2) with (6).

Corollary 3B. Let there be two parallel segments AB and ab which are parts of two closed circuits ABCD and abcd carrying currents I and i respectively. Let the lengths of these segments be L and l , and let them be separated by a distance r such that r Ll (Figure 2a). Then between these two segments there will be (i) a force of attraction if their currents are in the same direction, (ii) a force of repulsion if their currents are in opposite directions. The magnitude of this force, in either case, is approximately given as


FIirm ≈

μπ

0

2l

. (8)

Note that the expression above ignores the length L of the larger conductor.

3 Experiment No. 1: The Fundamental Experiment in Magnetism − Equivalence between a Bar Magnet and a Current Carrying Solenoid

To a school child magnetism means phenomena associated with “magnets”. He has seen magnets in different shapes, e.g., bar magnets, horse-shoe magnets, fridge magnets

(used to stick paper the fridge door), has played with them for fun and is familiar with some of their properties, e.g., that they attract iron. Yet when we teach magnetism to a beginner, our teaching strategy demands a paradigm shift from magnets to electric currents. The first lesson on magnetism should start with the field produced by an electric current and the force such current exerts on another current. This means that it is the Fundamental 1 that should form the basis for all subsequent discourses on magnetism.

Figure 3: Solenoidal compass and its accessories. The first lesson in magnetism should

therefore start by first establishing the Equivalence between a Bar magnet and a Current Carrying Solenoid by demonstrating that a current carrying solenoid replicates all the properties of a bar magnet, viz., (1) it has a north-seeking pole and a south-seeking pole, (2) it attracts iron and (3) like poles repel and unlike poles attract. We have designed the Solenoidal Compass and its Accessory to meet

precisely this teaching objective. We have designed the Solenoidal Compass

and its Accessory to demonstrate what we shall call the Fundamental Experiment in Magnetism, aimed at establishing the above equivalence. We had presented a detailed account of the device, and its pedagogical uses in an earlier article.4 Therefore we shall avoid further discussion of this experiment. We have, however, presented a schematic diagram of the


revised design of this device in Figure 3 and a still from a UGC TV program in Figure 4.

Figure 4. Still from a UGC TV program.

Figure 5. Schematic design of the apparatus for demonstration of the transverse

nature of the magnetic force.


4 Experiment No. 2: The Transverse Nature of Magnetic Force

One can give a convincing demonstration of the transverse nature of the magnetic force using one of those olden day cathode ray tubes. In this apparatus the electrons leave a trace of their path by ionizing the residual air inside the evacuated glass tube. When a bar magnet is brought close to this tube, its axis being held perpendicular to the path of the electrons, the ray is deflected giving a clear indication that the magnetic force is perpendicular to the velocity of the electrons.

However, such an experiment will not come under the “home-made” category. The home-experiment that we have fabricated is described schematically in Figure 5. It uses a rectangular coil W made of 70 turns of winding wire, and provided with heat sinks S1 and S2 in the form of thin aluminium foils stitched and glued to the coil. The electric current enters through the terminal P1 and leaves through the terminal P2 (Figure 5a).

The horizontal segment HH at the bottom of this coil is placed between the N-pole of the top magnet M1 and the S-pole of bottom magnet M2 of the magnet assembly shown in Figure 5b. This assembly is made of a pair of commonly available ceramic magnets (available in kids’ toy shops), each about 4 cm long. To hold them together we have used a single lamina collected from the choke of a fluorescent tube (whose multifarious uses had been highlighted in one of our previous articles2). With some sawing, trimming and gluing we have given it the shape shown in the figure.

The force experienced by the segment HH placed in the B field between M1 and M2 when a current of 0.5A flows through the coil is sufficiently large for the purpose of our experiment since the effective current is Ieff = 0.5A × 70 turns = 35A. We have two modes of placing the segment HH between the pole

pieces as shown in Figsure 5c and d. In the first mode the B field is vertical, and the segment HH suffers horizontal deflection, i.e., left or right. In the second mode the B field is horizontal and the segment HH suffers vertical deflection, i.e., up or down.

In order to hold the rectangular coil in place we have a platform (Figure 5e) and a spring-lever assembly (Figure 5f). Two vertically fixed aluminium strips AC and BD are electrically connected through the ports A and B to the DC power supply PS#1 (Figure 5g). The horizontal pins C and D (Figure 5e) transmit the voltage to the coil through the spring lever assembly. The lever consists of two parallel aluminium strips each having four holes and separated from each other by insulating plastic stubs inserted through the holes E and F and glued to them. The lever is supported on the pins C and D at the holes J1 and J2. The other two holes K1 and K2 have been used for supporting the rectangular coil by its pins P1 and P2, thereby transmitting the voltage from PS#1 to the rectangular coil.

The “pins” P1, P2, C and D are made of silver plated copper wire of diameter 1.5 mm. The rectangular coil of Figure 5a has been fabricated using 70 turns of 35 gauge winding wire around a wooden block cut to the required size, and then gluing them together with a thin thread and an adhesive (Araldite).

The complete assembly is shown in Figure5g. An actual photograph of the device is shown in Figure 6.

The experimental set-up proposed in this section gives a qualitative demonstration of the Corollary 2B written in the form of Eq.(2). In both modes of operation (see previous page) the vector L is horizontal and perpendicular to the vector B so that the magnitude of the magnetic force is Fm = IeffLB, where Ieff ≈ 35A and L ≈ 6.5 cm.

5 Experiment No. 3: Demonstration of Attraction/Repulsion Between Parallel/


Anti-parallel Currents; Measurement of the Force of Attraction, and Approximate Evaluation of μ0.

The device here is a Swinging Coil Cs suspended vertically and deflecting in the magnetic field B of a Horizontal Coil Ch. The objective of this device is two-fold. (1) It demonstrates attraction/repulsion between two parallel wires when the currents flowing in them are in the same/opposite directions (Corollary 3B). (2) It gives an approximate evaluation of the coupling constant μ0/4π from observation of the angle of deflection θ.

A schematic design of the device is shown in Figure 7a. The multi-line rectangle ABCD

represents the coil Cs. It has Ns = 60 turns of 35 gauge winding wire. Its terminals are soldered to two horizontal supporting pins S and S made of 1.5 mm brass rods. They rest on two holes drilled into a pair of inclined aluminium bars K and K which are firmly fixed to a flat wooden base. Leads from the DC power supply PS#1 are connected to the bars K and K thereby providing electric current Is (of about 1 A) flowing through this coil. In order to dissipate the heat generated by this current a heat sink HS1 (not shown in the drawing) made of thin aluminium foil is stitched to Cs.

Figure 6: A photograph of the apparatus for demonstration of the transverse nature of the magnetic force. C = Rectangular Current Carrying Coil, M1 and M2 = top and bottom magnets, F = Lever frame, L= lamina supporting the magnets, P = Platform.

The other rectangle EFGH represents Ch. It

has Nh = 300 turns of wire of the same gauge. The DC Power supply PS#2 provides current Ih of the order of 0.75A. It is loosely clamped to the heat sink HS2 made of aluminium plate (Figure 7b). The plate is bent at the edges to

make walls on three sides EF, EH and FG (we have shown only one of these walls, running parallel to EF, and labelled W). With this design HS2 serves three objectives. (1) The primary objective of dissipating the heat generated by Ih. (2) The walls on the sides EH


and FG provide “handle” for sliding Ch forward and backward (we have provided two parallel wooden guide walls so as to prevent sidewise movement of the plate) in order to bring the segment EF of Ch close to the segment AB of Cs, either during repulsion or during attraction. (3) The wall W makes a barrier so that the closest approach between the arms AB of Cs and EF of Ch is a “fixed distance” r.

At the top of the vertical arm BC of the coil Cs a pointer is provided. In the “attraction” mode, this pointer moves against an angular scale giving a visual measure of the deflection θ in degrees.

Figure 8 shows an actual photograph of the device with the coil Cs deflected by an angle of approximately 30 degrees.

Figure 7. Schematic design of the apparatus for measurement of μ0 using ”swinging coil”.

In the discussion to follow Cs and Ch will

mean the parallel arms AB and EF, respectively, of the two coils. When the currents Is and Ih are in opposite directions the force Fm between Cs and Ch is repulsive, so that Cs swings away from Ch, tilting towards the inclined bars KK.

When the currents are in the same direction this force is attractive. Consequently, Cs swings towards Ch and presses against W. By sliding Ch the angle of deflection of Cs with the vertical is allowed to increase until Cs separates from W at some angle θ. This θ is the required angle of deflection for currents Is and Ih. The three values θ, Is and Ih are required for evaluation of μ0.

Figure 9 explains the geometrical and other parameters used in deriving the formula for μ0. The coil Cs has mass M, G is its centre of gravity, w is its width. It swings about the line SS which is at a distance h above G. Taking the distance between the centres of the coil segments AB and EF to be r, and assuming that w is less than the length d of Ch, the magnetic field produced by Ch along the axis of AB is obtained from Eq. (6) to be

BN I

rh h≈ μπ0 2

. (9)

For the force between the coils we adopt Eq. (8).


F N I wBN N I I w

rm s ss h s h= ≈ ⎛

⎝⎜⎞⎠⎟

μπ0

42

. (10)

The force Fm makes the coil Cs tilt by an angle θ at which the torque due to the force of gravity Fg = Mg balances the torque due to the magnetic force Fm. Hence at equilibrium

Mghsinθ = Fmucosθ. (11)

Combining (11) with (10) we get an approximate formula for determination of μ0.

μπ

θζχ0

4 2≈

⎡

⎣⎢

⎤

⎦⎥

⎛

⎝⎜

⎞

⎠⎟ =

MghrN N wu I Ih s h s

tan , (12)

Figure 8. A photograph of the ”swinging coil” apparatus.

where ζ χθ

=⎡

⎣⎢

⎤

⎦⎥ =

⎛

⎝⎜

⎞

⎠⎟

MghrN N wu I Ih s h s2

; tan .

It should be remembered that the assumption behind the “approximate formula” (12) which is based on (8) is not valid (since the two coils are nearly equal.) Applying a more “adequate formula”5 which takes care of the magnetic force between all the four arms of the swinging coil Cs and all the four arms of

the horizontal coil Ch one gets a better estimate of μ0/4π.

We have tabulated (Table 1) below our experimental data and “estimates” of the value of of μ0/4π using both the “approximate” formula and as well as the “adequate formula” in Table 1, for the sake of comparison with the correct value given in Eq. (4). (We have taken g = 9.8m/s2.)


Figure 9. Explaining the measurement of μ0 using a “Swinging Coil”.

Table 1. Parameters and variables for the “Swing Coil” experiment.

M (gm)

h (cm)

r (cm)

w (cm)

u (cm)

Nh

Ns

ζ (×10−7Ν)

8.9 0.8 1.0 8.0 4.5 300 60 0.55 Ih

(A) Is

(A) θ

(deg) tanθ χ

(A−2) μo/4π(approx)

(×10−7Ν/Α2) μo/4π(adequate)

(×10−7Ν/Α2) 0.34 1.1 26 .4877 1.30 0.702 1.026 0.35 1.13 26 .4877 1.23 0.663 0.970 0.38 1.13 27 .5095 1.19 0.638 0.934

6 Experiment No. 4: Demonstration and Measurement of the Magnetic Field Inside a Solenoid, Leading to Evaluation of μ0

The experiment we are going to describe is a modification of the “current balance” described in PSSC Physics.6 The current balance has a U-shaped conducting path etched on one half of a rectangular flat plastic plate. A small mass m is placed at the end of the other half of the plate. The etched end of the plate is inserted inside a large solenoid. The plate is supported along its transverse axis by two horizontal brass rods. Currents Is and Iu flowing through the solenoid and the plate respectively are adjusted for

balancing the mass m, leading to evaluation of μ0. This experiment forms part of a PSSC kit that had been distributed across our country about 50 years ago.

Our experiment replaces the U-shaped conducting path (allowing a single layer of current) with a rectangular coil having 160 turns (thereby allowing 160 layers of current), so that we can get better effect with much less current drawn from our DC power supply. Also we have replaced the cylindrical solenoid with a solenoid with rectangular cross section for greater freedom of movement of the coil inside it. We shall describe our experiment.

The mention of “solenoid” normally brings us the picture of a cylinder with circular cross section and windings around it, thanks to


innumerable diagrams we have seen in text books. However, under the usual assumption that the B field is concentrated mostly inside the solenoid and is approximately uniform, the strength of Bin averaged across the cross section should be nearly independent of the shape of the cross section (unless the cross section has some “odd shape”). Under the

above assumption the magnetic field Bin inside the solenoid is approximately given as

BINLin ≈

μ0 , (13)

where I, N, L represent the current, number of turns and the length of the solenoid.

Figure 10. Schematic design of the apparatus for measurement of μ0 using ”rectangular coil inside rectangular solenoid”.

We have devised an experimental set up in

which a solenoid Σ with rectangular cross section has been used (Figure 10a). One reason for this choice is that rectangular aluminium pipes are abundantly available in local aluminium shops and such pipes come handy for acting as the frame on which the solenoid is to be wound. Also this aluminium base makes an excellent heat sink to dissipate the heat generated by the current Is which will flow through the coil. The strongest reason however is that when the rectangular coil Ρ (marked abcd in the diagram) is inserted inside the solenoid for detection of the Bin field, its right hand end, marked cd, will find greater freedom to move up and down under the magnetic force Fm as the current Ir will flow through it. A

circular cross section would have obstructed this movement due to its curved wall.

Our solenoid Σ is hand-wound with Ns = 1160 turns of 29 gauge winding wire on a 10 cm long rectangular frame cut out from a 6.3 cm×3.7 cm aluminium pipe (Figure 10b). The field Bin is created by the current Is that flows through Σ when the terminals are connected to the DC Power supply PS#1.

The average of the magnetic field Bin generated inside the solenoid by the current Is will be directed parallel to the axis. We have designed a rectangular coil Ρ having Nr = 160 turns of 35 gauge winding wire to sense this field (Figure 10c). The wire is first hand-wound on a 12.3 cm × 4.8 cm and about 0.5 cm thick rectangular wooden plate (so that the


dimensions of Ρ is slightly larger, i.e., about 12.6 cm×5.1 cm.) The coil is then removed from the frame and sewed onto a thick aluminium foil with thread after curling and wrapping up the edges of the foil around the coil (Figure 10d). The foil serves several purposes. (1) It acts as a heat sink. (2) It provides some rigidity to the coil Ρ by acting as a frame. (3) It provides a platform on which a counterbalancing mass m is to be placed. (4) It provides a means for fixing two insulated

vertical pins P and Q (we have used the ubiquitous pins used by clerks for fastening papers) for acting as the terminals to which the voltage from the DC Power supply PS#2 is transmitted. This is achieved by first soldering the ends of the coil Ρ to P and Q, and then resting these pins on two “bridge shaped” aluminium bases Ω - Ω (with grooves indented on it) which are electrically connected to the DC Power Supply PS#2.

Figure 11. Photograph of the apparatus for measurement of μ0 using ”rectangular coil inside rectangular solenoid”.

The polarities of the wires drawn from the power supplies PS#1 and PS#2 are chosen in such a way that Bin is directed from left to right and the current Ir is directed away from us, i.e., in the direction of cd (Figure 10 a). As a consequence the magnetic force Fm on the right cross-arm cd will be downward. To counterbalance this force a small mass m is placed on the aluminium foil just inside the left arm 4-1. (We have incorrectly shown m outside in Figure 10a for convenience of drawing, but

shown the correct position in Figure 10c). Initially the left end cross-arm ab is resting

on a wooden block ‘W’ and the arm bc is horizontal. The mass m is placed close to the cross-arm ab just inside the coil on the aluminium foil. PS#1 is switched on so that a steady current Is flows through Σ. Next, PS#2 is switched on and the current flowing through Ρ is gradually increased until, at some current Ir the right hand end just dips downward. These


two currents Ir and Ir are noted for determination of μ0/4π.

We have presented a photograph of the device in Figure 11.

Let us take l for the length of the cross-arm cd of Ρ which experiences the magnetic force Fm and L for the length of the solenoid Σ. The magnetic force Fmis obtained by combining Eqs. (2) and (9). Its magnitude is then

F B N IN I N I

Lm in r rs r r r= ≈ll

μ0 (14)

Assuming that the pins P and Q are located midway between the ends ab and cd, the gravitational force mg that balances Fm has the same magnitude. Hence, Fm = mg.

We shall use “small weights” for m in the range of 1-3 gm. Therefore we define the parameter η as follows.

Figure 12. IsIr versus m.

ηπ

= × −gLN Ns r4

10 3

l, (15)

with the explicit understanding that the masses of the counterweights will be in grams. Then

μπ

η0

4=

mI Is r

. (16)

The data obtained from our experiment have been tabulated in Table 2.

Table 2. Values of parameters and variables for “Coil-inside-Solenoid” experiment.

l (cm)

L (cm)

Nr Ns η (×10−7)

m (gm)

Is (A)

Ir (A)

IsIr (A2)

5.0 8.5 160 1160 0.0714 1 0.38 0.25 .095 2 0.39 0.45 .1755 3 0..39 0.65 .2535

For evaluation of μ0/4π we plotted IsIr

versus m as shown in Figure 12. The data shown in Table 2 on a straight line having a small positive intercept on the IsIr axis. The slope that the straight line makes with the vertical axis is the ratio x/y equal to 12.8. From this we find the experimental value μ0/4π = 12:8×.0714×10–7 = 0:914×10–7 N/A2.

Acknowledgements

The author is indebted to Mr. Vinay Babu and Prof. S.R. Madhu Rao for their constant assistance in overcoming all problems with his computer (used for preparing the manuscript). He is grateful to Prof. R. Srinivasan for his encouragement and for being instrumental in


providing the author with a small grant from the Meera Memorial Trust, Palghat, Kerala. Unfortunately the author could utilize only a small part of that grant within the stipulated time period. The cooperation received from Mr B. N. Nanjundaswamy, even though it was for a brief period, is also thankfully acknowledged. It was at his suggestion that the author used rectangular solenoid for Expt. No.4. The author is also grateful to Prof. S.R. Madhu Rao for going through the first draft of the manuscript and pointing out some errors. The author has used the digital camera presented by his son-in-law Michael Murphy for preparing Figures 6, 8 and 11.

The author has used LATEX2 “for composing this manuscript, has used free-software like Xfig 3.2.5, Gimp 2.2 (one of the packages in Debian Linux) for preparing the drawings, for editing the digital photographs and for incorporating these into the text of the manuscript. The anonymous authors of such software have been an inspiration for him to serve the physics community with his own kind of service without expecting a reward.

References

1. S. Datta, “Concept-centred experiments in physics”, Physics Education, Vol. 18, No.2, pp.123-142 (1993).

2. S. Datta, “Low cost electromagnetic induction kits out of the condemned chokes of fluorescent tubes”, Physics Education, Vol. 2, No.3, pp. 35-41 (1985).

3. W. Kaplan, Advanced Calculus, Addison Wesley, Reading (1952), p.261.

4. S. Datta, “Solenoidal compass and its uses in teaching magnetism”, Physics Education, Vol.10, No.2, pp. 137-142 (1993).

5. S. Datta, “Magnetic Torque Between a Rectangular Horizontal Coil and a Rectangular Swinging Coil”, to be published.

6. Physical Science Study Committee, Physics (2nd Edition), Originally published by D. C. Heath and Company, Boston. Indian Edition published by the National Council of Educational Research and Training, New Delhi (1966). See pp. 564-65.

Teaching Magnetism with Home-Made Experiments

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