26 Mar, 2013
PRESENTATION: The objective of converting mechanic energy to electric energy has always been a challenge for humans in the past. To accomplish it we’ve decided to resuscitate the first electromagnetic generator of the history: Faraday’s Disk.
- Unconventional Dynamo, Wojciech Dindorf, Phys. Teach. 40, 220 (2002)
- Building a cheap simple generator, David T. Kagan and Robert Keith, Phys. Teach. 37, 248 (1999)
INTRODUCTION: The system is based on the fact that a conductive material describing a movement in a space region where a magnetic field exists is submitted to a magnetic force which provokes a redistribution of the charge in its interior, phenomenon which translates onto the apparition in this of a difference of potential which can be used to generate a continuous electric current. In order to do that, we’ve based on the model developed by Faraday.
OBJECTIVE: To achieve electric energy from mechanic energy, 2 copper plates.
MATERIALS: Wood board, thin aluminum disc, steel bar, multimeter, 2 magnets.
SETUP: First, with the wooden planks, we create a base shaped as a U, which is high enough to place the disk inside it. Afterwards, we make a couple of holes in the sides, taking care that they are aligned. We introduce the bar with the disc through those holes and then we fix them with a pair of screws, in such a way that the disc is stuck to one side of the support, to place the magnets easily. We place one of the copper plates in contact with the disk and the other touching the steel bar. We connect both plates to the multimeter using cables and place the magnets on both sides of the disc, in such a way that the poles are opposed facing at each other. To finish, we fix both magnets, one to the lateral wall of the base and the other to some type of external support.
EXPLANATION: the disc like all good conductors has charges that can move freely in it. When the disc turns, its charges (dq) move jointly with it describing a circular path and with a speed tangential to the mentioned path. The existence of an external magnetic field, preferably to optimize the functioning of a perpendicular disc, enables the system to be used as electric generator.
All charge in movement immerse in a magnetic field experiments a strength which provokes an acceleration, perpendicular both to the path and to the magnetic field.
The magnetic field will provoke a redistribution of the charges from the center of the disc to its border. A process that will stop when the electric force which arises between them compensates its magnetic force:
Fm=dq v x B
Summing up Fm=Fe and therefore the electric field will be E=vB. As v=ω r, it results that E = ωrB, supposing the optimal conditions, B perpendicular to the disc.
The difference of the potential between the centre and the border of the disc ΔV is consequently (meaning that there is no internal resistance) equivalent to the e.m.f. ε:
being R the disc radius.
CONCEPTS: magnetic force, electromotive force, conductivity, transformation of energy, electric field, magnetic field.
- T. Valone, The Homopolar Handbook: A Definitive Guide to Faraday Disk & N-Machine Technologies, Integrity research institute,1994.
- I.M. Gottlieb, Practical Electric Motor Handbook, Elsevier, 1997.
- A. Pérez Gisbert , Ingeniería del medio ambiente, Editorial Club Universitario, 2010.
STUDENTS 2011-2012: César García, Iván Garrido, Andrés Gilsanz
LINK pdf STUDENTS (In Spanish):