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. In a nonlinear medium, the permeability can depend on the strength of the magnetic field. Permeability as a function of frequency can take on real or complex values. B is related to the Lorentz force on a moving charge q: H is related to the magnetic dipole density.
Where μ0 = 4π × 10−7 N A−2. Magnetisation curve for ferromagnets (and ferrimagnets) and corresponding permeability where . 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". Modern interest in the concept stems from particle theories, notably the grand unified and superstring theories, which predict their existence.[3][4] 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. where.
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). Since a vector field is quite difficult to visualize at first, in elementary physics one may instead visualize this field with field lines.
From the definition of the magnetic vector potential A and the fundamental theorem of the curl the magnetic flux may also be defined as: Magnetic field. Magnetic field of an ideal cylindrical magnet with its axis of symmetry inside the image plane. The magnetic field is represented by magnetic field lines, which show the direction of the field at different points. In everyday life, magnetic fields are most often encountered as an invisible force created by permanent magnets which pull on ferromagnetic materials such as iron, cobalt or nickel and attract or repel other magnets. Magnetic fields are very widely used throughout modern technology, particularly in electrical engineering and electromechanics. The Earth produces its own magnetic field, which is important in navigation.
Rotating magnetic fields are used in both electric motors and generators. History[edit] One of the first drawings of a magnetic field, by René Descartes, 1644. Three discoveries challenged this foundation of magnetism, though. Extending these experiments, Ampère published his own successful model of magnetism in 1825. Definitions, units, and measurement[edit] 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. Electromagnetic radiation. The electromagnetic waves that compose electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized EMR wave propagating from left to right. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The two types of fields in EMR waves are always in phase with each other with a fixed ratio of electric to magnetic field intensity.
Electromagnetic radiation (EM radiation or EMR) is a form of radiant energy, propagating through space via electromagnetic waves and/or particles called photons. In a vacuum, it propagates at a characteristic speed, the speed of light, normally in straight lines. EMR is emitted and absorbed by charged particles. In classical physics, EMR is considered to be produced when charged particles are accelerated by forces acting on them. Physics[edit] Theory[edit] Maxwell’s equations for EM fields far from sources[edit] Electromagnetic induction. Electromagnetic induction is the production of a potential difference (voltage) across a conductor when it is exposed to a varying magnetic field. It is described mathematically by Faraday's law of induction, named after Michael Faraday who is generally credited with the discovery of induction in 1831.
History[edit] A diagram of Faraday's iron ring apparatus. Change in the magnetic flux of the left coil induces a current in the right coil.[1] Electromagnetic induction was discovered independently by Michael Faraday and Joseph Henry in 1831; however, Faraday was the first to publish the results of his experiments.[2][3] In Faraday's first experimental demonstration of electromagnetic induction (August 29, 1831[4]), he wrapped two wires around opposite sides of an iron ring or "torus" (an arrangement similar to a modern toroidal transformer). Faraday explained electromagnetic induction using a concept he called lines of force.
Faraday's law and the Maxwell–Faraday equation[edit] where. Electromagnetic field. The field can be viewed as the combination of an electric field and a magnetic field. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field.
The way in which charges and currents interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law. From a classical perspective in the history of electromagnetism, the electromagnetic field can be regarded as a smooth, continuous field, propagated in a wavelike manner; whereas from the perspective of quantum field theory, the field is seen as quantized, being composed of individual particles. [citation needed] Structure of the electromagnetic field[edit] The electromagnetic field may be viewed in two distinct ways: a continuous structure or a discrete structure. Continuous structure[edit] Classically, electric and magnetic fields are thought of as being produced by smooth motions of charged objects.
Electrical resistance. An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area. All materials show some resistance, except for superconductors, which have a resistance of zero. The resistance (R) of an object is defined as the ratio of voltage across it (V) to current through it (I), while the conductance (G) is the inverse: may be most useful; this is called the "differential resistance".
Introduction[edit] The hydraulic analogy compares electric current flowing through circuits to water flowing through pipes. When a pipe (left) is filled with hair (right), it takes a larger pressure to achieve the same flow of water. In the hydraulic analogy, current flowing through a wire (or resistor) is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe.
Conductors and resistors[edit] Substances electricity can flow through are called conductors. Where. Permittivity. A dielectric medium showing orientation of charged particles creating polarization effects. Such a medium can have a higher ratio of electric flux to charge (permittivity) than empty space In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how much electric field (more correctly, flux) is 'generated' per unit charge in that medium. More electric flux exists in a medium with a high permittivity (per unit charge) because of polarization effects.
In SI units, permittivity ε is measured in farads per meter (F/m); electric susceptibility χ is dimensionless. Where εr is the relative permittivity of the material, and ε0 = 8.8541878176.. × 10−12 F/m is the vacuum permittivity. Explanation[edit] Vacuum permittivity[edit] Its value is[1] where If. Electric field. Electric field lines emanating from a point positive electric charge suspended over an infinite sheet of conducting material. Qualitative description[edit] An electric field that changes with time, such as due to the motion of charged particles producing the field, influences the local magnetic field. That is: the electric and magnetic fields are not separate phenomena; what one observer perceives as an electric field, another observer in a different frame of reference perceives as a mixture of electric and magnetic fields. For this reason, one speaks of "electromagnetism" or "electromagnetic fields". In quantum electrodynamics, disturbances in the electromagnetic fields are called photons.
Definition[edit] Electric Field[edit] Consider a point charge q with position (x,y,z). Notice that the magnitude of the electric field has dimensions of Force/Charge. Superposition[edit] Array of discrete point charges[edit] Electric fields satisfy the superposition principle. Continuum of charges[edit] Electrical conductivity. Definition[edit] Resistors or conductors with uniform cross-section[edit] A piece of resistive material with electrical contacts on both ends. where R is the electrical resistance of a uniform specimen of the material (measured in ohms, Ω) is the length of the piece of material (measured in metres, m) A is the cross-sectional area of the specimen (measured in square metres, m2).
The reason resistivity is defined this way is that it makes resistivity an intrinsic property, unlike resistance. In a hydraulic analogy, passing current through a high-resistivity material is like pushing water through a pipe full of sand, while passing current through a low-resistivity material is like pushing water through an empty pipe. The above equation can be transposed to get Pouillet's law (named after Claude Pouillet): The resistance of a given material will increase with the length, but decrease with increasing cross-sectional area. The formula and General definition[edit] Conductivity is the inverse: [edit] Electric current. Flow of electric charge In the International System of Units (SI), electric current is expressed in units of ampere (sometimes called an "amp", symbol A), which is equivalent to one coulomb per second.
The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ).[4]: 15 Electric current is also known as amperage and is measured using a device called an ammeter.[2]: 788 Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers. In ordinary conductors, they cause Joule heating, which creates light in incandescent light bulbs. Time-varying currents emit electromagnetic waves, which are used in telecommunications to broadcast information. Symbol Conventions The conventional direction of current, also known as conventional current,[10][11] is arbitrarily defined as the direction in which positive charges flow.
Reference direction . Ohm's law Alternating and direct current Occurrences Vacuum. Electric charge. Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. There exist two types of electric charges, called positive and negative . Positively charged substances are repelled from other positively charged substances, but attracted to negatively charged substances; negatively charged substances are repelled from negative and attracted to positive. An object will be negatively charged if it has an excess of electrons , and will otherwise be positively charged or uncharged. The SI unit of electric charge is the coulomb (C), although in electrical engineering it is also common to use the ampere-hour (Ah), and in chemistry it is common to use the elementary charge ( e ) as a unit.
The symbol Q is often used to denote a charge. The study of how charged substances interact is classical electrodynamics , which is accurate insofar as quantum effects can be ignored. [ edit ] Overview [ edit ] History [ edit ] Properties and. Capacitance. Capacitance is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance. A common form of energy storage device is a parallel-plate capacitor. In a parallel plate capacitor, capacitance is directly proportional to the surface area of the conductor plates and inversely proportional to the separation distance between the plates.
If the charges on the plates are +q and −q respectively, and V gives the voltage between the plates, then the capacitance C is given by which gives the voltage/current relationship The capacitance is a function only of the geometry (including their distance) of the conductors and the permittivity of the dielectric. For many dielectrics, the permittivity, and thus the capacitance is independent of the potential difference between the conductors and the total charge on them. The SI unit of capacitance is the farad (symbol: F), named after the English physicist Michael Faraday. Capacitors[edit] where , etc.