Faraday's Dynamo
Faraday's dynamo is sometimes quoted as an analogy for the Earth's supposed internal dynamo. The Faraday motor/dynamo when used as a motor is a copper disc with a direct current supply connected between the edge of the disc and its centre. When used as a dynamo, the output is taken from the centre of the disc and its edge. A magnetic field is applied at right angles to the plane of the disc near its edge. When power is applied to the motor between its axis and its periphery, a current flows at right angles to the magnetic field. The interaction of the magnetic field and the current causes the disc to rotate as a motor.. Rotation of the same disc as a dynamo creates a current from the periphery to the axis. That is to say that the current produced by the dynamo is in the opposite direction to that which occurs when it is used as a motor. If the dynamo/motor had a magnetic field aligned with the disc's axis to simulate the orientation of the Earth's magnetic field, the device would not function as a dynamo or motor.

Perpetual Motion (Electric Current)
On rechecking my sources I found an image that proves that astronomers have very little idea about the way magnetism and electricity work. There was a drawing that was intended to show how a Faraday dynamo could be connected to provide a self maintaining current. I have reproduced the drawing idea here with added colour and a magnet.

It is, in a sense, a sort of perpetual motion machine so I have given it that title. Lenz's Law states that there is NO WAY that a magnet induced current in a conductor can act to sustain itself. The drawing as shown just short circuits the output of the dynamo. The only effect of the short circuit would be to increase the mechanical power required to rotate the disc. There is no way of making a connection that will sustain the current induced by the motion of the disc between the poles of the magnet. Lenz's Law states that the magnetic field generated by an induced current in a conductor will be in opposition to the magnetic field that induced the current. If there was a way to create a current in a magnetic field that created a magnetic field of the same polarity as the original magnetic field, it would be the first creation of an electrical perpetual motion machine. The concept in mechanical terms is the equivalent of a downhill skier who converts potential energy into kinetic energy through gravity who then somehow converts his kinetic energy back into potential energy to be used again.

For Electronic Engineers
Those of you who have studied electronics will know that when doing analysis of an electric circuit, it is usual to draw an equivalent circuit to show current paths. It would seem that no astronomer has ever tried to draw an equivalent circuit for the theoretical Earth Dynamo System that is claimed to be the source of the Earth's magnetism. If they had, they would have concluded that the Earth Dynamo Theory is untenable.

The Shape of the Earth's Magnetic Field
The shape of the Earth's magnetic field is similar to the shape of an apple. Assume that the magnetic field at the Earth's equator at the Earth's surface corresponds to the skin of the apple around its middle. Now imagine a thin ring conductor all around the equator that rotates with the Earth. The conditions are similar to that of the Faraday dynamo. As with the Faraday dynamo, any current generated is radial. In a thin ring it could not go very far. If the ring is made into a disc which extends from the centre of the Earth to its surface, a current which starts at the surface progresses radially towards the Earths centre. But, at the Earth's centre, there is a magnetic field that operates in the other polarity. A current which starts at the centre progresses outward towards the surface. As the magnetic fields which create these currents are parts of the same magnetic system, they cancel out. Note that the centre of the Earth is NOT magnetic. The metals iron and nickel are too hot to keep their magnetic properties.

An experiment with a bar magnet under a sheet of paper with iron filings scattered on the paper shows the shape of the magnetic field.

The two dimensional image is not unlike the shape of half an apple sliced through its core. The lines created by the iron filings form flattened elliptical loops on either side of the magnet. The lines seen are not magnetic lines of force but the result of the way that iron filings behave in a magnetic field. Filings that are roughly in line with the axis of the magnet have an induced north south magnetism; the south pole of one filing attracts the north pole of the next filing so that chains of filings form lines from one pole of the magnet to the other. These chains become like very long and thin magnets. Since each chain becomes a long thin magnet with the same polarity as its neighbour, there is a repulsive force between adjacent chains which keeps them apart. This phenomenon is responsible for the so-called magnetic lines of force. If the bar magnet, paper and iron filings experiment is conducted many times, it will be found that the lines of iron filings occur in different places. This means that there are either an infinite number of lines that are so close together that they cannot be distinguished from each other or that there are no lines at all.

The Apparent Reversal of a Bar Magnet's Magnetic Field
Some people may not comprehend why the magnetic field at the centre of the Earth is of the opposite polarity to the field at the surface near the equator. On Earth we have compasses for navigation. One end of a compass needle points towards the north magnetic pole and the other end points towards the south magnetic pole. The north seeking end of a compass needle is referred to as a "North" pole of the compass by convention. If the "South" pole of a bar magnet is put near the compass, the north seeking pole of the compass will be attracted to it. From this it can be concluded that the magnetic pole at the north of the Earth is in fact of the same polarity as the south pole of a bar magnet. In the iron filings experiment it must therefore be concluded that the north seeking ends of the filings point towards the south pole of a bar magnet. If the bar magnet south pole is regarded as up, the north seeking pole (red in the sketch) of a compass near the end of the magnet will be pointing downwards. At the other end of the magnet the north seeking pole will also be pointing downwards because the south seeking pole (blue in the sketch) will be pointing upwards. It can be seen from the compass orientations in the sketch that a path formed by the iron filings forms most of a near elliptical loop with the north seeking ends of the filings always pointing around the loop. Along the axis of the bar magnet the north seeking pole of a compass points downwards while it points upwards at the side of the bar magnet. The magnetic field strength along the axis of the bar magnet is concentrated while it is dispersed away from the sides of the magnet. But, since the magnet has only one magnetic field, the sum of the magnetic influences at the axis must equal the sum of the magnetic influences around it. Now, hopefully, it can be seen that an imaginary conducting disc that extends from the centre of the Earth to the equator and beyond is subject to equal and opposite magnetic influences at its centre and its periphery. The spinning disc would produce opposite currents from the centre outwards and from the periphery inwards. The same rule applies no matter how thick the disc is. The maximum thickness for such a disc is the distance between the north and south geographic poles of the Earth. In practice this means a sphere with a bar magnet at its axis of rotation. As with a Faraday dynamo with a bar magnet aligned through its axis, instead of between its axis and its periphery, no net current is generated.

A reply to a query concerning Michael Faraday's dynamos 28/01/2008
It has been observed in the vacuum of a Cathode Ray Tube that a changing magnetic field moves electrons sideways.
This is shown in the web page sunmgnt2.htm .
Electrons in a wire are less easily observed but they behave in a similar manner.
If a magnet is moved towards a wire that is in a circuit, the electrons in the wire move sideways forming an electric current. If the wire is formed into a loop, and a bar magnet is pushed into the loop, the sideways movement of the electrons goes around the loop.
If the wire is wound in a coil of many loops, the currents in the loops add together forming a stronger current.
Michael Faraday made a coil of many loops that was connected to a simple current indicator. He found that when a bar magnet is pushed into the coil, the indicator showed current while the magnet was being pushed into the coil. The current stopped when the magnet stopped moving. When the magnet was pulled out of the coil, a current going the other way was detected.

Michael Faraday discovered that it did not matter which moved, the coil or the magnet. The effect was the same. He therefore tried to devise a way to make a piece of wire to move continuously in a magnetic field to produce a continuous current. This gave rise to what became the Faraday disc dynamo. (See sketch at the top of this page.) A metal disc can be considered to be made up of thousands of radial wires all connected together. When the disc is rotated in a magnetic field, the effect is like one piece of wire always moving in the same direction in the magnetic field. It therefore produces a continuous current. A later version of the dynamo used a rotating switch called a commutator that effectively arranged that a rotating coil of wire was moved in one direction in a magnetic field for a moment then disconnected. Then the rotating switch connected another identical coil of wire as it moved through the magnetic field in the same way. This system did not produce a continuous current but a series of pulses of current which always flowed in the same direction. The rotating switch contacts arranged that each coil was only connected when it was going through the magnetic field in the correct direction. The rotating coils and the rotating switch were fixed to the same shaft so that there would be a continuous train of pulses of current that flowed in the same direction.
In very many situations the pulses of current were as useful as a continuous current. There is a sketch of a motor on my website which is very similar to a dynamo.

Faraday discovered that a dynamo and a motor are effectively the same thing. Mechanical energy turns a dynamo to produce electricity and electrical energy makes a motor turn to produce mechanical energy.
Current that always flows in one direction is called direct current. The fact that the current is produced as as series of pulses is of no significance in most applications.

Copyright © 6th September 2005, 1st July 2006 & 29/01/2008