Self Inductance

Self inductance is the ration between the induced Electro Motive Force (EMF) across a coil to the rate of change of current through this coil. Self inductance is related term to self induction phenomenon. Because of self induction self inductance generates. Self-inductance or Co-efficient of Self-induction is denoted as L. Its unit is Henry (H). First we have to know what self induction is. Self induction is the phenomenon by which in a coil a change in electric current produces an induced Electro Motive Force across this coil itself. This induced Electro Motive Force (ε) across this coil is proportional to the current changing rate. The higher the rate of change in current, the higher the value of EMF.

We can write that, self inductance equation self inductance equation But the actual equation is The question is that why there is Minus (-) sign? This Induced EMF across this coil is always opposite to the direction of the rate of change of current as per Lenz’s Law. self inductance When current (I) flows through a coil some electric flux produces inside the coil in the direction of the current flowing. At that moment of self induction phenomenon, the induced EMF generates to oppose this rate of change of current in that coil. So their values are same but sign differs. Look at the figure below. self inductance Take a closer look at a coil that is carrying current. The magnetic field forms concentric loops that surround the wire and join to form larger loops that surround the coil. When the current increases in one loop the expanding magnetic field will cut across some or all of the neighboring loops of wire, inducing a voltage in these loops.

Video Presentation of Self Inductance

For the DC source, when the switch is ON, i.e. just at t = 0+, a current will flow from its zero value to a certain value and with respect to time there will be a rate of change in current momentarily. This current produces magnetic flux lines (φ) through this coil. As current changes its value to zero to a certain value that’s why magnetic flux (φ) get rate of change with respect to the time, i.e. Now apply Faraday's Law in this coil, Where, N is the number of turn of the coil and e is the induced EMF across this coil. Lenz's law states that an induced current due to induced EMF has a direction such that its magnetic field opposes the change in magnetic field that induced the current. As per Lenz’s law we can write down this equation of induced voltage across the coil, Now, we can modify this equation to calculate the value of inductance of a coil. so, [B is the flux density i.e. B =φ/A, A is area of the coil], [N. φ or L.I is called magnetic flux Linkage and it is denoted by Ѱ] Again, H.l = N.I, where H is the magnetizing force due to which magnetic flux lines flow from south to north pole inside the coil, l is the effective length of the coil and r is the radius of the coil cross-sectional area. self inductance L is a geometric quantity; it depends only on the dimensions of the solenoid, and the number of turns in the solenoid. Furthermore, in a DC circuit when the switch is just closed, then only momentarily effect of self-inductance occurs in the coil. After then no effect of self inductance is in a coil. It is because of steady flow of unidirectional current through this coil after closing the operating switch after t = 0+.

But in AC circuit, alternating effect of current always causes the self-induction in the coil and a certain value of this self-inductance gives the inductive reactance depending on the value of supply frequency. Generally in the electrical circuit the coils those are used are known as inductor having values of L1, L2, L3 etc. when they are series combination then equivalent inductance of them is calculated as self inductor in series When they are in parallel, then inductors in parallel self inductance


Closely Related Articles Mutual InductanceMore Related Articles Electric Current and Theory of Electricity | Heating and Magnetic EffectNature of ElectricityDrift Velocity Drift Current and Electron MobilityElectric Current and Voltage Division RuleRMS or Root Mean Square Value of AC SignalWorking Principle of a CapacitorQuality Factor of Inductor and CapacitorTransient Behavior of CapacitorCylindrical CapacitorSpherical CapacitorCapacitors in Series and ParallelHow to Test Capacitors?Electrical Conductance Conductivity of Metal Semiconductor and Insulator | Band TheoryWhat is Electrical Resistance?Resistivity and Laws of ResistanceProperties of Electric ConductorTemperature Coefficient of ResistanceResistance Variation with TemperatureSeries ResistanceActive and Passive Elements of Electrical CircuitElectrical DC Series and Parallel CircuitOhm's Law | Equation Formula and Limitation of Ohm's LawKirchhoff Current Law and Kirchhoff Voltage LawSingle and Multi Mesh AnalysisSuperposition TheoremThevenin Theorem and Thevenin Equivalent Voltage and ResistanceNorton Theorem | Norton Equivalent Current and ResistanceReciprocity TheoremNodal Analysis in Electric CircuitsMaximum Power Transfer TheoremDelta - Star transformation | Star - Delta TransformationMagnetic FieldMagnetic FluxMagnetic PermeabilityHysteresis LoopMagnetic Field and Magnetic Circuit | Magnetic MaterialsMagnetic SaturationEnergy Stored in a Magnetic FieldStatic Electric Field | Electrostatic Induction A Current Carrying Conductor Within A Magnetic FieldMagnetic SusceptibilityHard Magnetic MaterialsSoft Magnetic MaterialsMagnetic Circuit with Air GapElectric ChargeCoulombs Law | Explanation Statement Formulas Principle Limitation of Coulomb’s LawElectric Lines of ForceWhat is Electric Field?Electric Field Strength or Electric Field IntensityWhat is Flux? Types of Flux?Electric FluxElectric PotentialCapacitor and Capacitance | Types of CapacitorsEnergy Stored in CapacitorCharging a CapacitorDischarging a CapacitorFourier Series and Fourier TransformTrigonometric Fourier SeriesAnalysis of Exponential Fourier SeriesParity GeneratorElectric Circuit and Electrical Circuit ElementsSeries Parallel Battery CellsRL Series CircuitWhat is Inductor and Inductance | Theory of InductorRLC CircuitThree Phase Circuit | Star and Delta SystemRL Parallel CircuitRL Circuit Transfer Function Time Constant RL Circuit as FilterConstruction of AC Circuits and Working of AC CircuitsSeries RLC CircuitParallel RLC CircuitResistances in Series and Resistances in ParallelResonance in Series RLC CircuitPlanar and Non Planar Graphs of CircuitClipping CircuitSI System of UnitsElectrical International SymbolElectric Power Single and Three Phase Power Active Reactive ApparentVector Algebra | Vector DiagramRelationship of Line and Phase Voltages and Currents in a Star Connected SystemVector Diagram | Three Phase Vector DiagramTypes of Resistor Carbon Composition and Wire Wound ResistorVaristor Metal Oxide Varistor is Nonlinear ResistorCarbon Composition ResistorWire Wound ResistorVariable Resistors | Defination, Uses and Types of Variable ResistorsLight Dependent Resistor | LDR and Working Principle of LDRSource of Electrical EnergyVoltage SourceIdeal Dependent Independent Voltage Current SourceVoltage or Electric Potential DifferenceVoltage in SeriesVoltage in ParallelVoltage Drop CalculationVoltage DividerVoltage MultiplierVoltage DoublerVoltage RegulatorVoltage FollowerVoltage Regulator 7805Voltage to Current ConverterNew Articles Collecting Oil Sample from Oil Immersed Electrical EquipmentCauses of Insulating Oil DeteriorationAcidity Test of Transformer Insulating OilMagnetic FluxRing Counter