the production of aurora and magnetic storms" [..] ".. the rotation of a conductor in a magnetic field produces an electric field in the system at rest. This phenomenon is well known from laboratory experiments and is usually called 'homopolar ' or 'unipolar' induction. Unipolar inductors have been associated with the aurorae on Uranus, binary stars, black holes, galaxies, the Jupiter Io system, the Moon, the Solar Wind,<ref>Srnka, L. J., "Sheath-limited unipolar induction in the solar wind" (1975) Astrophysics and Space Science', vol. 36, Aug. 1975, pp. 177–204.</ref> sunspots,Osherovich, V. A.; Garcia, H. A., "Electric current in a unipolar sunspot with an untwisted field" (1990) Geophysical Research Letters (ISSN 0094-8276), vol. 17, Nov. 1990, pp. 2273–2276. and in the Venusian magnetic tail. Physics Like all dynamos, the Faraday disc converts kinetic energy to electrical energy. This machine can be analysed using Faraday's own law of electromagnetic induction. This law, in its modern form, states that the full-time derivative of the magnetic flux through a closed circuit induces an electromotive force in the circuit, which in turn drives an electric current. The surface integral that defines the magnetic flux can be rewritten as a line integral around the circuit. Although the integrand of the line integral is time-independent, because the Faraday disc that forms part of the boundary of line integral is moving, the full-time derivative is non-zero and returns the correct value for calculating the electromotive force. Alternatively, the disc can be reduced to a conductive ring along the disc's circumference with a single metal spoke connecting the ring to the axle. The Lorentz force law is more easily used to explain the machine's behaviour. This law, formulated thirty years after Faraday's death, states that the force on an electron is proportional to the cross product of its velocity and the magnetic flux vector. In geometrical terms, this means that the force is at right-angles to both the velocity (azimuthal) and the magnetic flux (axial), which is therefore in a radial direction. The radial movement of the electrons in the disc produces a charge separation between the center of the disc and its rim, and if the circuit is completed an electric current will be produced. See also Barlow's wheel Electric generator Electric motor Homopolar motor Faraday paradox Faraday's law of induction Wimshurst machine References General references Don Lancaster, "Shattering the homopolar myths". Tech Musings, October, 1997. (PDF) Don Lancaster,