Gaussian surface A cylindrical Gaussian surface is commonly used to calculate the electric charge of an infinitely long, straight, 'ideal' wire. A Gaussian surface is a closed surface in three-dimensional space through which the flux of a vector field is calculated; usually the gravitational field, the electric field, or magnetic field.[1] It is an arbitrary closed surface S = ∂V (the boundary of a 3-dimensional region V) used in conjunction with Gauss's law for the corresponding field (Gauss's law, Gauss's law for magnetism, or Gauss's law for gravity) by performing a surface integral, in order to calculate the total amount of the source quantity enclosed, i.e. amount of gravitational mass as the source of the gravitational field or amount of electric charge as the source of the electrostatic field, or vice versa: calculate the fields for the source distribution. Gaussian surfaces are usually carefully chosen to exploit symmetries of a situation to simplify the calculation of the surface integral.
The Solenoid and the Toroid Toroid is a hollow circular ring (like a medu vadai) on which a large number of turns of a wire are wound. The above figure represents a toroid wound with a wire carrying a current I. Consider path 1, by symmetry , if there is any field at all in this region, it will be tangent to the path at all point and will equal the product will equal the product of B and the circumference d = 2pr of the path. Similarly, if there is any field at path 3, it will also be tangent to the path at all points. The field of the toroidal solenoid is therefore confined wholly to the space enclosed by the windings. If we consider path 2, a circle of radius r, again by symmetry the field is tangent to the path and Each turn of the winding passes once through the area bounded by path 2 and total current through the area is NI, where N is the total number of turns in the windings. Using Ampere's law If the radial thickness of the core is small, field is almost constant across the section. = 0).
Magnetic flux Description[edit] The magnetic flux through a surface when the magnetic field is variable relies on splitting the surface into small surface elements, over which the magnetic field can be considered to be locally constant. The total flux is then a formal summation of these surface elements (see surface integration). Each point on a surface is associated with a direction, called the surface normal; the magnetic flux through a point is then the component of the magnetic field along this direction. The magnetic interaction is described in terms of a vector field, where each point in space (and time) is associated with a vector that determines what force a moving charge would experience at that point (see Lorentz force). A generic surface, S, can then be broken into infinitesimal elements and the total magnetic flux through the surface is then the surface integral where the line integral is taken over the boundary of the surface S, which is denoted ∂S. for any closed surface S. where Patents
Small Magnetic Receiving Loops Revised Dec 22, 2005 corrected text errors and reworded some areas to make clearer Revised June 13 2006 to add link. Related pages coaxial cable and especially skin depth (Please read the Radiation and Fields page) Small Receiving Loops Small loops are often referred to as "magnetic radiators". Nothing is further from the truth! Field Impedance The ratio of electric to magnetic field sensitivity is sometimes called or can be described as the "field impedance". Although fields have different ratios close to the antenna, at distances of about one wavelength the field impedances of small antennas are virtually indistinguishable from each other. Loop Antenna Fields It is the energy storage or reactive induction field response within λ/10 distance from the antenna that gives small "magnetic loop" and "electric dipole" antennas their names. Very close to a small loop antenna (but not necessarily near the open ends of the small loop where the tuning capacitor is) the magnetic field dominates.
Magnetic monopole It is impossible to make magnetic monopoles from a bar magnet. If a bar magnet is cut in half, it is not the case that one half has the north pole and the other half has the south pole. Instead, each piece has its own north and south poles. A magnetic monopole cannot be created from normal matter such as atoms and electrons, but would instead be a new elementary particle. A magnetic monopole is a hypothetical elementary particle in particle physics that is an isolated magnet with only one magnetic pole (a north pole without a south pole or vice-versa).[1][2] In more technical terms, a magnetic monopole would have a net "magnetic charge". Magnetism in bar magnets and electromagnets does not arise from magnetic monopoles, and in fact there is no conclusive experimental evidence that magnetic monopoles exist at all in the universe. Historical background[edit] Pre-twentieth century[edit] Twentieth century[edit] Since Dirac's paper, several systematic monopole searches have been performed. where
Robins can literally see magnetic fields, but only if their vision is sharp | Not Exactly Rocket Science Some birds can sense the Earth’s magnetic field and orientate themselves with the ease of a compass needle. This ability is a massive boon for migrating birds, keeping frequent flyers on the straight and narrow. But this incredible sense is closely tied to a more mundane one – vision. Katrin Stapput from Goethe University has shown that this ‘magnetoreception’ ability depends on a clear image from the right eye. The magnetic sense of birds was first discovered in robins in 1968, and its details have been teased out ever since. When cryptochrome is struck by blue light, it shifts into an active state where it has an unpaired electron – these particles normally waltz in pairs but here, they dance solo. The upshot is that magnetic fields put up a filter of light or dark patches over what a bird normally sees. To test the bounds of this ability, Stapput wanted to see what would happen if she blurred a robin’s vision. Reference: Current Biology
Permeability (electromagnetism) A closely related property of materials is magnetic susceptibility, which is a measure of the magnetization of a material in addition to the magnetization of the space occupied by the material. In electromagnetism, the auxiliary magnetic field H represents how a magnetic field B influences the organization of magnetic dipoles in a given medium, including dipole migration and magnetic dipole reorientation. Its relation to permeability is In general, permeability is not a constant, as it can vary with the position in the medium, the frequency of the field applied, humidity, temperature, and other parameters. B is related to the Lorentz force on a moving charge q: H is related to the magnetic dipole density. Relative permeability, sometimes denoted by the symbol μr, is the ratio of the permeability of a specific medium to the permeability of free space, μ0: where μ0 = 4π × 10−7 N A−2. Magnetisation curve for ferromagnets (and ferrimagnets) and corresponding permeability where from .
magnetic fields We will now deal with objects which are very commonly used in practical engineering fields.Although they are too much of idealization ,yet they are so important to know that the entire study of electrodynamics is incomplete without them.I expect Rohina and Rahul that you went through the reference for Gauss law I gave you. I will like you to take a brief review of Gauss law and Ampere's Law before we proceed any further.To begin lets consider a simple case of a wire of infinite length . Yes.By the BiotSavart law we can get the field at each point , but by clever deductions from the elements of symmetry we can predict the magnetic lines of force at a glance.In this case the magnetic fields have to be tangential and the magnitude has to be constant for same r(the modulus of r as in cylindrical coordinate system) Now my question is how will one predict the direction of magnetic lines of force around the wire ? (almost interrupting ) I know it ,Sir, its the right hand rule. That's good ! .