inductance (grob)

• inductance is the ability of a conductor to produce induced voltage when the current varies
• A long wire has more inductance than a short wire
• AC circuits


  current is continuously changing and producing induced voltage
• DC circuits in which the current changes in value

  A steady direct current that does not change in value is not affected by inductance, however, because there can be no induced voltage without a change in current.
• When the direct current is changing between zero and its steady value, the inductance affects the circuit at the time of switching. This effect of a sudden change is called the circuit’s transient response.
• For the same number of turns and frequency, which has more inductance, a coil with an iron core or one without an iron core?

  a coil with an iron core
• Joseph Henry 


  invention of the electric motor and the development of the first electromagnetic telegraph, which formed the basis for the commercial telegraphic system
• The ability of a conductor to induce voltage in itself when the current changes is its self-inductance or simply inductance
• The symbol for inductance is L, its unit is the henry (H)
• the faster the current changes, the higher the induced voltage because when the flux moves at a higher speed, it can induce more voltage
• coils are often called inductors
• self inductance


  the changing current and the opposition where they're both happening in the same coil so the coil is sort of opposing itself
• more inductance, more ability to resist changes in the current
• inductance "electrical inertia" resistance to change of current
• inductor has no problem with the current, its the change in current that the inductor has a problem
• if inductance value is very high then it would take longer time for the current to rise its maximum value because the opposition would be so much stronger
• smaller the inductor produces more voltage than the inductance
• A greater number of turns N increases L because more voltage can be induced. L increases in proportion to N^2 . Double the number of turns in the same area and length increases the inductance four times
• More area A enclosed by each turn increases L. This means that a coil with larger turns has more inductance. The L increases in direct proportion to A and as the square of the diameter of each turn
• The L increases with the permeability of the core. For an air core, absolute permeability is 1. With a magnetic core, L is increased by the permeability factor because the magnetic flux is concentrated in the coil
• The L decreases with more length for the same number of turns because the magnetic field is less concentrated.
• Counter emf or back emf is also known as a bucking voltage
• By Lenz’s law, the induced voltage vL must produce current with a magnetic field that opposes the change of current that induces vL
• lenz law


  the orientation that is induced will produce a magnetic field that counteracts the change in flux
• lenz law


  flux in increasing the magnetic field that induced by the induced current should make the flux decrease
• lenz law


  if the flux is decreasing then the induced magnetic field by the induced current should make the flux decrease less or should be additive to the flux
• when di increases, vl has the polarity that opposes the increase of current
• di decrease, vl has the opposite polarity to oppose the decrease of current
• when current is increasing the voltage produces an opposing current
• for the opposite case when current is decreasing, voltage produces an aiding current
• Inductance, therefore, is the characteristic that opposes any change in current.
• mutual inductance


  When the current in an inductor changes, the varying flux can cut across any other inductor nearby, producing induced voltage in both inductors.
• mutual inductance


  the turns are linked by magnetic flux
• iron core increases the magnetic flux, since it concentrates magnetic flux
• any magnetic lines that do not link the two coils results in leakage flux
• The fraction of total flux from one coil linking another coil is the coefficient of coupling k between the two coils
• coefficient coupling increase by placing coils together by placing them parallel, when it is placed perpendicular there are no mutual conductance
• A high value of k, called tight coupling, allows the current in one coil to induce more voltage in the other coil
• Loose coupling, with a low value of k, has the opposite effect.
• In the extreme case of zero coeffi cient of coupling, there is no mutual inductance. Two coils may be placed perpendicular to each other and far apart for essentially zero coupling to minimize interaction between the coils.