Some texts refer to the northa€“seeking and southa€“seeking poles of a magnet, in an attempt to avoid some of the ambiguity that can arise when discussing the magnetic poles of the Earth. In recent years, studies of the conditions under which magnetic monopoles might be produced have indicated that extremely large amounts of energy would be required a€“ amounts which might have been available in the early stages of the evolution of the universe.
In Classical electromagnetic theory it is normally assumed that magnetic monopoles do not exist.
Electric fields, and the inverse_square_lawinverse square law of force between electric charges, (Coulomb’s law), are described elsewhere in FLAP. Remember, this only applies if the particle is moving at right angles to the magnetic field. Nikola Tesla (1856a€“1943) was a Sloveniana€“born American electrical engineer who made major contributions to high voltage engineering and to electric generator design. A straight line is said to be tangent_to_a_curvetangential to a curve at a certain point if it just touches the curve at that point, but does not cross it. In field plots such as for Questions T1 and T2 you will need to refer to Figures 6a and 6b and to use the general ideas on how to show the strength of a field using field lines.
Gadolinium (Gd) and dysprosium (Dy) are members of a group of elements known as the lanthanides or rare earths. To sinter means to convert a powder into a solid block of material by the simultaneous application of heat and pressure. An easy way to remember this is to visualize an arrow with the tip coming towards the viewer or the flights going away from the viewer. The field that results from the addition of the Earth’s field and the field from the wire will not have field lines that are truely circular, but if the current in the wire is sufficiently large the departure from circularity will be negligible. One of the simplest ways to demonstrate magnetism is to dip a magnet into a box of paper clips a€“ with care, you may succeed in picking up 20 or 30 clips. In Section 2 of this module, you will see how interactions between magnets are described in terms of magnetic poles and magnetic fields.
Section 3 describes how magnetic fields can also be produced by electric currents, as shown by Hans Christian Oersted (1777a€“1851) in 1820.
Study comment Having read the introduction you may feel that you are already familiar with the material covered by this module and that you do not need to study it.
You are given three apparently identical iron rods, but are told that two of them are permanently magnetized. Two concentric coils of wire are positioned with their planes perpendicular to one another.
These fields are as shown in Figure 23b (you may have these in different directions if the current in your coils were not the same as in (a), but your resultant field should still have the same magnitude). Study comment Having seen the Fast track questions you may feel that it would be wiser to follow the normal route through the module and to proceed directly to the following Ready to study? Alternatively, you may still be sufficiently comfortable with the material covered by the module to proceed directly to the Section 4Closing items. Study comment In order to study this module you will need little background knowledge of magnetism, beyond its occurrence. Which of the following quantities are vectors and which are scalars: density, energy, force, speed, temperature, velocity and weight? When an electric current flows in a copper wire, what type of charged particle moves in the wire to constitute that current? A particle is subjected to two forces, each of the same magnitude_of_a_vector_or_vector_quantitymagnitude F, acting simultaneously.
Most of us are familiar with some simple applications of magnets and magnetism around the home which make use of the attractive force between small magnets and unmagnetized pieces of steel. A more ancient application of magnetism than any of the above examples can be seen in the compass. The pattern of attraction of small iron or steel objects to a bar magnet shows that the strongest magnetic forces occur near the ends of the magnet.
Since a compass needle adopts a particular orientation when no other magnets are near, the implication is that the Earth itself must have magnetic properties. The concept of a magnetic pole is of great value in qualitative discussions of magnetic forces, but it is not particularly useful in quantitative work. Before leaving the subject of magnetic poles its worth noting one further point, even though it relates to matters far beyond the scope of FLAP.
The fact that magnets interact even when at a distance from one another is usually explained in terms of a magnetic field.
In physics the term field is generally used to denote a physical quantity to which a definite value may be ascribed at each point in some region of space at a given time.
Note that in this case the field is specified by a vector at every point a€“ a quantity with magnitude and direction a€“ and is therefore said to be a vector field.
Now the magnetic field in some region of space must describe magnetic forces, so we might reasonably expect it be a vector field, just like the gravitational and electric fields. Figure 4 An inclinometer or dip circle, used for measuring the angle of the Earth’s field with respect to the horizontal. Consequently, if we use a compass needle to define the direction of the field we must either make sure that the needle is free to rotate in three dimensions, or we must use two needles (one rotating horizontally and the other vertically) to determine the threea€“dimensional orientation at any point.
The direction of a magnetic field at any point is the direction of the magnetic force that would act on an isolated north magnetic pole (if we had one) placed at that point. But you shouldn’t expect to determine the field direction by this method in practice. Figure 5 The magnetic field of an isolated bar magnet represented (approximately) by magnetic field lines.
The direction of the field line at any point indicates the direction of the magnetic field at that point (i.e. The density of the field lines in any region is proportional to the magnitude of the magnetic field in that region. In practice the last of these conditions is quite hard to satisfy, especially if you are trying to represent a threea€“dimensional field (such as that of the Earth) on a flat piece of paper (as in Figure 2). In plotting the field of a magnet, as in Figure 5, we would not normally attempt to nullify the Earth’s field. There is one further important feature of field line plots: field lines will never be found to cross each other because that would imply that a compass placed at the crossa€“over point would have to point in two directions at once! Another method of finding the shape of the field pattern near a magnet is to cover the magnet with a horizontal sheet of paper and to sprinkle fine iron filings evenly over the paper. Sketch the magnetic field plots for a bar magnet in the Earth’s field with its Na€“pole pointing (a) north, and (b) west. We can think of the field lines as if they were fastened to the magnet in the region of the poles, so that when the magnet is rotated from position (a) to position (b), it appears that the field lines are pulled around with it. As was described earlier, a very simple test of the magnetic properties of different materials is to see if they are attracted by a magnet. If we place a bar magnet near to a rod of pure iron, then the rod and the magnet are attracted to one another.
Materials, such as pure iron, which depend (almost entirely) on the presence of another magnet for their magnetism are described as magnetically soft. Another group of magnetic materials, known as ferrites, are brittle ceramics made by sintering oxides i of iron and barium (Ba).
Scientific studies of the magnetic properties of materials are far more sophisticated than this brief discussion might indicate. With the understanding of atomic structure and quantum mechanics has come an appreciation that ferromagnetism and permanent magnetism have their origins almost entirely in the intrinsic properties of the electrons (electron spin magnetism) which make up their constituent atoms.
Should the materials used in the storage of information be magnetically soft or magnetically hard? The materials should be magnetically hard so that they retain the information in the absence of the magnetic field used to record it. In 1820, a Danish philosopher and scientist, Hans Christian Oersted, performed the first experiment to show an interaction between an electric current and a compass needle.
Oersted showed that a current in a wire could, in certain circumstances, cause the deflection of a compass needle placed nearby.
Figure 10 Circular magnetic field lines produced by a current in a long straight wire with the current pointing (a) downwards, and (b) upwards. Iron filings may also be used to show the field pattern, but this needs currents of some tens of amps (or several adjacent wires, each carrying more moderate currents in the same direction). In each case you will find that your fingers curl around your thumb in exactly the same way that the magnetic field lines curl around the current.
We can now use the righta€“hand grip rule to explain why Oersted obtained a compass deflection in some positions relative to the wire and not in others.
For the situation described in (b), where the wire is horizontal, then to the sides of the wire the field will be directed vertically upwards or downwards: a normal compass needle, being designed to rotate in the horizontal plane, cannot respond to such a vertical field. Figure 13 The field strength is the same at any point on the surface of a cylinder which is coaxial with the wire. If you imagine a set of coaxial cylinders drawn around the wire, as shown in Figure 13, the field strength is the same at all points on the surface of any one cylinder, but is different for each cylinder.
Second, notice that Equation 2 is not a vector equation a€“ it shows the magnitude of the field but not its direction. As noted earlier, the SI unit of the field strength B (r) is the tesla (abbreviated to T) and the SI unit of current is the ampere (A). Finally, we note one further point concerning the magnetic fields produced by current in straight wires.
For a bundle of wires each carrying a current, the resultant field will be approximately the same as if we had the same total current flowing in a single wire. Figure 16a Magnetic field components produced by small elements of a circular loop of wire. If we know the shape of the magnetic field due to a long straight wire carrying a steady current, it is fairly easy to build up pictures of the sort of magnetic fields that are produced by other configurations of current carrying wires. Figure 16b An accurate representation of a cross section of the field through a circular loop; the full field pattern comes from the rotation of the figure around the vertical axis of symmetry of the loop. To obtain a more accurate result, it is necessary to add vectorially all the small magnetic field components created by the various small sections of the wire. Even without deriving this equation it is easy to see that its form is physically plausible: the larger the current, the stronger the magnetic field that results. Suppose we take a single loop of wire (as in Figure 16b), and place a second loop parallel to the first and a short distance away, as in Figure 17a. We now extend our two loops of wire into a whole series of loops, arranged sequentially and pushed close together.
The resulting pattern of field lines is shown in Figure 18b for a loosely wound solenoid and in Figure 18c for a tightly wound solenoid. In other words, if the solenoid is very long then it is only the environment near to the point concerned which affects the field strength, and this is determined by the turns per unit length and the current in those turns (rather than the total number of turns).
Perhaps at this point we should take a little time to consider the use of words like long and short; Question T7 has already asked you to think about this.
It is clear that we cannot apply the expression for the field in a long solenoid to an ideal coil: if we were to put the length as zero in the denominator of Equation 4 we would obtain an infinite field strength. Now we will summarize all the expressions for the magnitudes of the magnetic fields generated by simple current geometries.
If we have a current carrying circuit of wire which includes a straight section, then there will be no contribution from that section to the magnetic field at any point along the projection of the axis of the straight section. While we are not able to prove this final quoted result now we can make it reasonable by the following argument. The boxed results above, together with the principle of superposition, allow us to deduce the magnetic field produced by various configurations of current, provided they can be related to the simple situations discussed above. From Figure 21, we see that there are two straight sections of wire (DA and BC) in which the current is directed towards and away from the point P.
Several times in this module we have referred to the fact that a magnet can be made using electric currents. In an electromagnet the current produces a magnetic field and this in turn induces strong magnetism in the ferromagnetic material within the coil or solenoid. There are many examples of everyday applications of magnetism, including the use of the magnetic compass in navigation. The centres of magnetic force in a bar magnet are located near the ends of the magnet and are known as the poles of the magnet. In practice this means a mass that is sufficiently small that it has a negligible effect on the field.
But beware, in specialized texts the term magnetic field strength is sometimes reserved for another quantity. The general case where the particle may be moving at any angle relative to the field is discussed elsewhere in FLAP. More formally, we can say that a curve and its tangent at a particular point have the same gradient at that point.
However, a full treatment of electron spin and the origins of magnetism is beyond the scope of FLAP. Notice that in general the field within a toroidal solenoid is not uniform (as it is for the case of the long straight solenoid), but varies with the radial distance from the centre of the toroid, being largest on the inside boundary. The objects around us divide broadly into two groups: those which are attracted by a magnet and those which are not.
You will learn how to plot magnetic field lines, using either iron filings or a compass needle, how to interpret such plots, and how to sketch the field lines of magnets in new orientations and positions.


This section then discusses the magnetic fields produced by electric currents in certain wella€“defined circuit configurations, namely a long straight wire, a circular loop of wire, a solenoid and a toroidal solenoid. Since unlike poles attract, then we must conclude that the Earth must have a south magnetic pole pointing towards the geographic North Pole and vice versa. If they repel each other, then you will know that they are both magnets, because repulsion can only occur between two like poles. The direction of the field produced at the centre of a coil is at right angles to the plane of the coil, therefore, as the coils are perpendicular, the fields they produce at their centres are also perpendicular. The module is not mathematically demanding because the formulae associated with magnetic fields are quoted and not proved. In what way does this movement differ from the electric_currentconventional current in the wire? The electrons move away from the negative terminal of a power supply and towards the positive terminal.
This is an example of the resultant_vectorresultant of two forces of equal magnitude acting at right angles. Steel tools are sometimes found to have acquired magnetic properties, as shown by their ability to attract iron filings or small screws or nails a€“ screwdrivers and cold chisels often exhibit this effect. As the north pole of a compass points approximately to the geographic north, the Earth must have a magnetic south pole near the geographic North Pole, as shown in Figure 2. The limitation arises from the fact that in practice it appears to be impossible to isolate either a north magnetic pole or a south magnetic pole. Even individual atoms or atomic constituents such as electrons and protons are magnetically similar to tiny bar magnets, not to isolated magnetic poles. At the present time many of the theories which aim to describe the nature of the fundamental constituents of all forms of matter, i.e.
This formula shows that the magnetic force between monopoles is expected to satisfy an inverse square law just like the electrostatic force between point charges. The main purpose of this subsection is to introduce magnetic fields and to explain how they can be determined. For example, the fact that a definite temperature can be associated with each point in the room you are now occupying means that there is a temperature field in the room. There are a number of ways in which it might be done, but in view of what was said earlier the most obvious is to use a compass. When dealing with the magnetic field of the Earth it has been traditional for centuries to use two needles. This is a sufficiently important combination of units that it is given its own SI name and symbol. Assuming that the proton is moving at right angles to the field at the point in question, what is the magnitude of the instantaneous magnetic force on the proton? For that reason most field line representations of magnetic fields are at best approximate.
Since the bar magnet essentially consists of two opposite magnetic poles of equal strength separated by a fixed distance it is sometimes described as a magnetic dipole, and the field that it produces is said to be a dipolar field. The observed field would therefore be the resultant vector sum of the fields of the Earth and the magnet. Figures 6a and 6b show extended plots when the magnet has its Na€“pole pointing south and east, respectively. This test provides an easy and immediate classification into materials which are strongly attracted and those which are not.
When, however, the bar magnet is removed, the iron retains (almost) none of its magnetic properties. In contrast, steels are examples of alloys made by adding other elements (typically carbon) to iron.
Granules of these ceramics can also be bonded with plastics or rubber to give flexible magnets (such as refrigerator seals) and are also used to make magnetic audio and video tapes, or floppy disks for computers. Research into the magnetic properties of materials has been, and continues to be, one of the most active areas of physics. This association of magnetic fields and currents provided the basis for a new branch of physical science a€“ electromagnetism. The greatest deflection was produced with the wire in a horizontal plane parallel to the undeflected needle and either above or below it. The fingers curl about the pointing thumb in the same sense as the field lines curl about the current. If you pass a vertical current carrying wire through a horizontal card on which you place a compass, then you can plot the magnetic field produced by the current. If the direction of current is reversed, then the direction of the field lines is also reversed, as is shown in Figure 10. Just close the palm of your right hand with thumb extended and point your thumb in the direction of the current shown in either diagram of Figure 10.
This simple way of remembering the direction of the magnetic field is illustrated in Figure 11 and is known as the righta€“hand grip rule.
The field it produces at the sides is vertical and the compass cannot respond but the field above and below is horizontal and the compass will be deflected, either to the W or to the E. At a perpendicular radial distance r from a long straight wire, the magnitude of the magnetic field vector (or the magnetic field strength), for which we use the symbol B (r), is proportional to the current I in the wire and inversely proportional to the distance r. It shows that if the current is increased, so is the strength of the field that it produces at a fixed distance from the wire.
A magnetic field is a vector field and we could write a more complicated vector equation which would fully describe both its magnitude and direction. For each of the points a, b and c, calculate the local magnetic field strength, and state whether the magnetic field points into or out of the plane of the paper. If we have a bundle of straight wires, all close together and each carrying a current in the same direction, then the total magnetic field produced at some point by the bundle will be the vector sum of the fields produced by the individual currents.
At any particular point on the wire, the field lines will be concentric circles about the wire, at least to the extent that the influence of other parts of the wire can be ignored, as shown in Figure 16a. The mathematics of such a sum is beyond the scope of this module, but the rough shape of the field pattern is clear from Figure 16b.
How would you expect the field pattern and the strength of the field at the centre to change if the single loop were replaced by a compact coil of N turns, all having the same radius as the single turn? At some distance away from the wires it would be difficult to distinguish between N turns of wire each carrying a current I and one turn carrying a current NI.
If the currents in the two loops circulate in the same sense, as shown, then the two loops produce similar fields at their centres. If each loop is connected to the adjacent loops, so that they form a single continuous coil, as illustrated in Figure 18a, then the coil so formed is called a solenoid and its shape is that of a helix. In the case of an infinitely long solenoid, the field strength is the same at all internal points. We would also expect the field at a point in the solenoid to increase if we brought the turns closer to the point a€“ this is achieved by making L smaller.
Provided we do not approach the ends of the solenoid, the field within it is uniform a€“ the field has the same strength at points immediately adjacent to the wires as it has in the centre. Words of this type are only meaningful if we are told, or can infer, some yardstick for comparison. The correct approach here is to regard the ideal coil as a multia€“turn loop, and to multiply the righta€“hand side of Equation 3 by the number of turns in the coil. Calculate the magnetic field strength at a point halfway between the axis of the solenoid and the windings.
So the strength at a point midway between the axis and the winding is exactly the same as the field strength at any other point inside the solenoid. Suppose we take a long solenoid and curl it up so that the solenoid itself forms a single circular loop. Figure 20b shows a very long toroidal solenoid, with the toroidal radius RT which is much larger than the coil turns radius RC.
What are the maximum and minimum values of the magnetic field inside the coils when a current of 1.5 A flows through the wires? Movement of electric charge constitutes a current and it is this current which gives rise to magnetic fields.
In the sense that a coil or solenoid carrying a current produces a magnetic field, these devices behave as magnets.
This induced magnetism then enhances considerably the magnetic forces from the coil or solenoid alone. A freelya€“suspended bar magnet aligns itself northa€“south, and its poles are known as the north and south poles. This section of the module also includes a discussion of magnetic dipoles and monopoles, and ends with an overview of magnetic properties of materials. Using the right-hand grip rule and the principle of superposition, it shows how the field patterns from more complicated current configurations can be built up. If you are sure that you can meet each of these achievements, try the Subsection 4.3Exit test. You will however need to be familiar with the following terms: density, electric charge, electric current, energy, force, scalar, speed, temperature, vector, velocity and weight. The scalars are: density, energy, speed (which is the magnitude of the velocity) and temperature. Historically however, an electric current was first defined as the movement of positively charged particles, i.e. Many refrigerator doors are held closed by magnetic forces, though in this case the magnetized material, often a special ceramic powder, is dispersed in a rubber or plastic strip around the door opening and the steel of the door itself is attracted to the strip. If, for instance, you cut a bar magnet in half, instead of obtaining two separate magnetic poles you will simply produce two small bar magnets, each with a north pole and a south pole (see Figure 3).
Our inability to completely separate north and south poles contrasts sharply with the relative simplicity of separating positive and negative electric charges and means that magnetic phenomena have to be treated somewhat differently from the electrical phenomena with which they otherwise have a great deal in common. This is said to be a scalar field since its value at any point (at a particular time) is determined by a single scalar quantity a€“ the temperature T at that point. But in the absence of isolated magnetic poles (the magnetic equivalent of masses and charges) how are we to specify the magnitude and direction of this field? We know that a compass needle tends to take on a specific alignment in the presence of a magnet, so we can define the direction of a magnetic field at any point as the direction indicated by the north pole of a compass needle placed at that point.
The angle between the Earth’s magnetic field and the horizontal at any point is called the angle of inclination or the angle of dip and the device that uses a vertically rotating needle to measure that angle is called a dip circle or an inclinometer (Figure 4). Once the direction of a magnetic field has been determined at some point, or better still in some small region, it is easy to place a wire at right angle to the field and to send an electric current through that wire. Figure 5 makes no attempt to show the threea€“dimensional nature of the field; it is restricted to the plane of the page. Note that there are regions where the fields of the Earth and the magnet are almost equal and opposite, so the resultant field is very weak and the field lines correspondingly far apart.
This similarity between the lines of filings and field line patterns can be very misleading as it may be interpreted as meaning that the magnetic field exists only along these lines, and that at points in between the lines there is no field.
The direction of the field is the same at every point, and is everywhere parallel to the field lines. The former group has been found to consist primarily of five elements a€“ iron (Fe), cobalt (Co), nickel (Ni), gadolinium (Gd) and dysprosium (Dy) i a€“ and some associated alloys. We say that these magnetic properties are induced in the iron rod by the bar magnet, that is to say that the magnet’s field causes the rod to change temporarily into a magnet.
These materials are harder to magnetize, but once they are magnetized they do not easily become demagnetized.
Information is recorded on tapes or disks by magnetizing their ferromagnetic grains through the application of a localized external magnetic field that is generated by, and is proportional to the strength of, the signal being recorded. International conferences entirely devoted to magnetism are held on a regular basis and there is a very large annual output of books and scientific papers dealing with magnetic materials. Electromagnetism is a major topic within physics and in this module we are able only to give the briefest of introductions to it. Oersted also found the important result that reversing the current reversed the direction of the deflection. We will, instead, rely on the righta€“hand grip rule to tell us the field direction in this simple situation.
This is an example of the principle of superposition a€“ which is an extension of a familiar result concerning forces. Of course, in the real world, the points on the wire cannot be considered in complete isolation and the pattern of field lines sketched in Figure 16a is therefore only an approximation. For example, in the centre of the loop the fields due to each individual part of the wire reinforce one another, with all the field lines pointing downwards through the middle of the loop.
The fields are in the same direction and combine in the region of their centres to produce a continuous field, as in Figure 17b. If an experiment requires some object to be placed in a uniform magnetic field, then one way of achieving this is to place the object inside a long solenoid, keeping it away from the ends where we would expect some decrease in the field.
When we say that a solenoid is long and no other object is mentioned, then our only item of comparison is another dimension of the solenoid a€“ the radius (or diameter). This doughnut shape, shown in Figure 20a, is called a toroid or a torus and a coil wrapped around it is a toroidal solenoid.
This might be expected for a toroidal solenoid of sufficiently large toroidal radius since an enlarged view of a small section of such a solenoid would appear to be almost straight and very long. Imagine an observer positioned in line with a current flowing towards or away from the observer.


We can dramatically increase the magnetic strength of such a device by wrapping the coil or solenoid around a core of ferromagnetic material, such as iron. If the ferromagnetic material is magnetically soft then when the current ceases so too does the magnetism, although a small amount may remain in the ferromagnetic material to the extent that it is not fully soft. In the case of the paper clips, the property of magnetic attraction is transferred by magnetic induction from the magnet to the nearest clips, which themselves then act as magnets and attract further clips. The formulae for the magnetic field strengths produced by these basic current configurations are given, allowing the numerical calculation of these field strengths in various situations. If you have difficulty with only one or two of the questions you should follow the guidance given in the answers and read the relevant parts of the module. If they now repel each other, then they are the magnets, and the unused rod is unmagnetized. You will also need to be familiar with vectorvector notation, including magnitude_of_a_vector_or_vector_quantitymagnitude of a vector, and the idea of combining vectors in one and two dimensions, using the triangle_ruletriangle or parallelogram_ruleparallelogram rules and simple trigonometry. Magnets are also to be found in television sets, electric motors, microwave ovens and loudspeakers.
A freely suspended bar magnet, or compass, will rotate to an approximately northa€“south line, but always the same pole points in the same direction. The Earth’s magnetic poles are close to, though not exactly coincident with, its geographic poles.
It is this difference that accounts for a good deal of the mathematical complexity that arises in the description of magnetism. This sounds like an eminently sensible way of defining the direction of a magnetic field, though we actually need to be think a little more about the details if we are to use it in a wide range of circumstances.
When this is done it is easy to show that the magnetic field exerts a force on the current carrying wire.
Furthermore it is only an approximate representation of the field; the field lines near the mida€“point of the magnet have been drawn with roughly equal separations, indicating that the field is of uniform magnitude in that region whereas in reality the magnitude of the field would actually decrease as the distance from the magnet increased. In fact, using a compass, we can follow a field line anywhere we like in the vicinity of a magnet (provided our starting point is not one at which the the field is zero) because the field is continuous from point to point. In Figure 7b, the greater density of field lines at the right of the diagram indicates that the magnitude of the field is greater there.
Further observation shows that the force between the magnet and the rod is always one of attraction, from which we deduce that the induced pole at the near end of the rod is always of the opposite polarity to the adjacent end of the magnet. Such materials are said to be magnetically hard and are the materials from which permanent magnets are made.
The stored information can be erased with a strong magnetic field, allowing the tape or disk to be reused.
With a sufficiently large current these loops are circles concentric with the wire, as shown in Figure 10. Equation 2 has a very simple form because the field produced by this current is highly symmetrical a€“ the field strength at any point is determined by the perpendicular distance from the wire. If several forces act on a body at the same time, then the resultant force is the vector sum of those forces taken one at a time.
So, a long solenoid has a length much greater than its diameter, and a short solenoid is one which has a length less than its diameter.
What is the magnetic field strength at the centre of the solenoid if the current in the separate loop flows (a) in the same direction and (b) in the opposite direction to the current in the solenoid?
We should not be surprised by this result for, after all, a toroidal solenoid is just a solenoid which has been made to join up with itself and might be thought of as having infinite length because it has no ends!
The charge flow has no velocity component across the line of sight and the observer will therefore be unaware of the motion of the charge and will observe no magnetic field. The flexibility of the electromagnet, as opposed to a permanent magnet, is that its strength is variable and controllable. However, if you have difficulty with more than two of the Exit questions you are strongly advised to study the whole module.
If they still attract, you must have selected only one magnet, but you will not know which it is.
If you are uncertain about any of these terms then you can review them now by reference to the Glossary, which will also indicate where in FLAP they are developed. So we speak of the conventional current and think of this as consisting of positive particles flowing. We therefore distinguish between the poles by calling the one that points north a north_magnetic_polenorth pole (usually written N-pole) and the other a south_magnetic_polesouth pole (S-pole). Such monopoles have never been convincingly detected, despite one or two claims to the contrary, and it is widely believed that even if they do exist they are so rare that they are never likely to be observed.
For instance, if dealing with a magnetic field that changes direction over a small region of space (such as the magnetic field inside an electronic device) we would have to use a very tiny compass indeed, so we should really imagine that we are determining the direction with a vanishingly small compass that can effectively show us the direction of the field at a point.
The current in the wire is composed of moving charged particles, and the force that acts on the wire is one manifestation of the general observation that a magnetic field exerts a force on any moving charged particle, provided the particle is not travelling parallel to the field.
Nonetheless, the diagram gives a clear (and correct) impression that the field of the dipole is the vector sum of the fields from the poles at either end of the magnet. The apparently significant lines of filings are quite fortuitous and arise through the existence of a few, perhaps larger, filings which are more reluctant to move when the paper is tapped, and so provide a centre to which other filings are attracted. Materials which are apparently unaffected by a magnet do in fact have weak magnetic properties, some are actually repelled by a magnet, but such effects are seen only with very sensitive apparatus and we will not discuss them further. The study of permanent magnetism is an area of great technological importance, but one with unexpected results. For example, as you will see later in this section, the field of a bar magnet can be reproduced using current in a coil. If the forces are produced by the magnetic fields of several different currents, then the resultant force can be found by adding the forces due to the separate currents a€“ in other words, the resultant magnetic field is the vector sum of the individual magnetic fields due to the separate currents. Electromagnets have very widespread applications, ranging from tiny earphones to huge cranes for lifting magnetic materials. The direction of the field at any point indicates the direction in which an isolated north magnetic pole placed at that point would tend to move (or the direction in which the north pole of a freely suspended compass needle would point). To find out, take one of your selected pair and go through the same procedure using it and the third rod.
The following questions will allow you to establish whether you need to review some of these topics before embarking on this module. In the case of current in a copper wire, a negative charge flowing in one direction is exactly equivalent (i.e.
Moreover, we need to be aware that the magnetic field at a given location may point in any direction; it is not necessaily horizontal. The general relationship between the magnetic field B at a point, the velocity υ of an electrically charged particle as it passes through that point, and the magnetic force Fmag that acts on the particle is a little complicated so we will not discuss it here. If we put the rod in contact with the magnet, it acts like an extension of the magnet and it, in turn, can attract a further rod and so on, but with the strength of the attractive forces becoming weaker, as we go further from the magnet. For example, the simple addition of small amounts of copper (a nona€“ferromagnetic material) to carbon steel produces magnets of much greater strength.
If the ferromagnetic material within a coil is magnetically hard then the material may become permanently magnetized. This is a familiar result a€“ a permanent magnet can lift a chain of nails or pins (Figure 9), but when the magnet is forcibly removed from the first nail or pin, the rest fall. The induced magnetism is only temporary, and disappears when the inducing field is removed.
THESE VERY SAME ENFORCEMENT AGENCIES, WHO HAVE SWORN TO PROTECT AND SERVE, OUR COUNTRY, AND CITIZENS ,ARE BUT SOME, OF THE CORRUPT,GREEDY TRAITORS .ENGAGED IN THE TYRANNY AND TORTURE. The school district has moved to a biometric identification program, saying students will no longer have to use an ID card to buy lunch.A  BIOMETRICS TO TRACK YOUR KIDS!!!!!i»?i»?A TARGETED INDIVIDUALS, THE GREEDY CRIMINALS ARE NOW CONDONING THEIR TECH! Paul Weindling, history of medicine professor at Oxford Brookes University, describes his search for the lost victims of Nazi experiments. The chairman of the board at ESL a€” then proprietor of the desert wasteland in Nevada known as a€?Area 51a€? a€” was William Perry, who would be appointed secretary of defense several years later.
EUCACH.ORG PanelIn a 2-hour wide-ranging Panel with Alfred Lambremont Webre on the Transhumanist Agenda, Magnus Olsson, Dr.
Henning Witte, and Melanie Vritschan, three experts from the European Coalition Against Covert Harassment, revealed recent technological advances in human robotization and nano implant technologies, and an acceleration of what Melanie Vritschan characterized as a a€?global enslavement programa€?.Shift from electromagnetic to scalar wavesThese technologies have now shifted from electromagnetic wave to scalar waves and use super quantum computers in the quantum cloud to control a€?pipesa€? a reference to the brains of humans that have been taken over via DNA, via implants that can be breathed can breach the blood-brain barrier and then controlled via scalar waved on a super-grid. Eventually, such 'subvocal speech' systems could be used in spacesuits, in noisy places like airport towers to capture air-traffic controller commands, or even in traditional voice-recognition programs to increase accuracy, according to NASA scientists."What is analyzed is silent, or sub auditory, speech, such as when a person silently reads or talks to himself," said Chuck Jorgensen, a scientist whose team is developing silent, subvocal speech recognition at NASA Ames Research Center in California's Silicon Valley. We numbered the columns and rows, and we could identify each letter with a pair of single-digit numbers," Jorgensen said. People in noisy conditions could use the system when privacy is needed, such as during telephone conversations on buses or trains, according to scientists."An expanded muscle-control system could help injured astronauts control machines.
If an astronaut is suffering from muscle weakness due to a long stint in microgravity, the astronaut could send signals to software that would assist with landings on Mars or the Earth, for example," Jorgensen explained. These are processed to remove noise, and then we process them to see useful parts of the signals to show one word from another," Jorgensen said.After the signals are amplified, computer software 'reads' the signals to recognize each word and sound.
Our Research and Development Division has been in contact with the Federal Bureau of Prisons, the California Department of Corrections, the Texas Department of Public Safety, and the Massachusetts Department of Correction to run limited trials of the 2020 neural chip implant. We have established representatives of our interests in both management and institutional level positions within these departments. Federal regulations do not yet permit testing of implants on prisoners, but we have entered nto contractual agreements with privatized health care professionals and specified correctional personnel to do limited testing of our products. We need, however, to expand our testing to research how effective the 2020 neural chip implant performs in those identified as the most aggressive in our society. In California, several prisoners were identified as members of the security threat group, EME, or Mexican Mafia.
They were brought to the health services unit at Pelican Bay and tranquilized with advanced sedatives developed by our Cambridge,Massachussetts laboratories.
The results of implants on 8 prisoners yielded the following results: a€?Implants served as surveillance monitoring device for threat group activity. However, during that period substantial data was gathered by our research and development team which suggests that the implants exceed expected results. One of the major concerns of Security and the R & D team was that the test subject would discover the chemial imbalance during the initial adjustment period and the test would have to be scurbbed. However, due to advanced technological developments in the sedatives administered, the 48 hour adjustment period can be attributed t prescription medication given to the test subjects after the implant procedure. One of the concerns raised by R & D was the cause of the bleeding and how to eliminate that problem.
Unexplained bleeding might cause the subject to inquire further about his "routine" visit to the infirmary or health care facility. Security officials now know several strategies employed by the EME that facilitate the transmission of illegal drugs and weapons into their correctional facilities. One intelligence officier remarked that while they cannot use the informaiton that have in a court of law that they now know who to watch and what outside "connections" they have. The prison at Soledad is now considering transferring three subjects to Vacaville wher we have ongoing implant reserach. Our technicians have promised that they can do three 2020 neural chip implants in less than an hour. Soledad officials hope to collect information from the trio to bring a 14 month investigation into drug trafficking by correctional officers to a close. Essentially, the implants make the unsuspecting prisoner a walking-talking recorder of every event he comes into contact with. There are only five intelligence officers and the Commisoner of Corrections who actually know the full scope of the implant testing.
In Massachusetts, the Department of Corrections has already entered into high level discussion about releasing certain offenders to the community with the 2020 neural chip implants. Our people are not altogether against the idea, however, attorneys for Intelli-Connection have advised against implant technology outside strick control settings. While we have a strong lobby in the Congress and various state legislatures favoring our product, we must proceed with the utmost caution on uncontrolled use of the 2020 neural chip.
If the chip were discovered in use not authorized by law and the procedure traced to us we could not endure for long the resulting publicity and liability payments. Massachusetts officials have developed an intelligence branch from their Fugitive Task Force Squad that would do limited test runs under tight controls with the pre-release subjects. Correctons officials have dubbed these poetnetial test subjects "the insurance group." (the name derives from the concept that the 2020 implant insures compliance with the law and allows officials to detect misconduct or violations without question) A retired police detective from Charlestown, Massachusetts, now with the intelligence unit has asked us to consider using the 2020 neural chip on hard core felons suspected of bank and armored car robbery. He stated, "Charlestown would never be the same, we'd finally know what was happening before they knew what was happening." We will continue to explore community uses of the 2020 chip, but our company rep will be attached to all law enforcement operations with an extraction crrew that can be on-site in 2 hours from anywhere at anytime.
We have an Intelli-Connection discussion group who is meeting with the Director of Security at Florence, Colorado's federal super maximum security unit.
The initial discussions with the Director have been promising and we hope to have an R & D unit at this important facilitly within the next six months.
Napolitano insisted that the department was not planning on engaging in any form of ideological profiling. I will tell him face-to-face that we honor veterans at DHS and employ thousands across the department, up to and including the Deputy Secretary," Ms. Steve Buyer of Indiana, the ranking Republican on the House Committee on Veterans' Affairs, called it "inconceivable" that the Obama administration would categorize veterans as a potential threat.



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Rubric: Electromagnetic Pulse Shield



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