Self Inductance - Definition and Formula

Self Inductance - Definition and Formula

In this post, we will cover Self Inductance Definition and Self Inductance Formula that will help you to understand Self Inductance better.

Self Inductance Definition-

When a coil carries a current it establishes a magnetic flux. When the current in the coil changes, the magnetic flux linking with the coil also changes. It is observed that this change in the value of current or flux in the coil is opposed by the instantaneous induction of opposing emf. This property of the coil by which it opposes the change in the value of current or flux through it due to the production of self-induced emf is called Self-inductance. It is measured in terms of co-efficient of self-inductance L. It obeys Faraday's law of electromagnetic induction like any other induced emf.


Self Inductance Definition

Self Inductance Formula-

For a given coil (provided no magnetic material such as iron is nearby) the magnetic flux linked with it will be proportional to the current, i.e.

where L is called the self-inductance (or simply inductance) of the coil. The induced emf is given by-
Self Inductance Formula

Unit of Self Inductance-


The SI unit of inductance is henry (symbol H), henry is a big unit of inductance, Smaller units millihenry (mil) and microhenry (pH) are used.

Thus, the self-inductance of a coil is 1 H if an induced emf of 1 volt is set up when the current in the coil changes at the rate of one ampere per second.

The role of self-inductance in an electrical circuit is the same as that of the inertia in mechanical motion. Thus the self-inductance of a coil is a measure of its ability to oppose the change in current through it and hence is also called electrical inertia.




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Mutual Inductance - Definition and Formula

Mutual Inductance

In this post, we will cover Mutual Inductance Definition and Mutual Inductance Formula that will help you to understand Mutual Inductance better.

Mutual Inductance Definition-

Whenever a change in current occurs in a coil, an induced emf is set up in the neighboring coil. This process is called mutual induction. The coil in which the emf is induced is called the secondary coil. 


Mutual Inductance
Explanation of Mutual Induction

If a current I(1) flows in the primary coil, the magnetic flux linked with the secondary coil will be-
where M is called mutual inductance between the two coils or circuits.


Mutual Inductance Formula-

The electromotive force induced in the secondary coil is given by-
Thus the mutual inductance of a pair of circuits is 1 H if a rate of change of current of one ampere per second induces an emf of I V in the other circuit.


Learn More About Mutual Inductance - Mutual Inductance Wikipedia


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Magnetic Field Intensity - Unit and Formula

Magnetic Field Intensity

This post is all about Magnetic Field Intensity, its definition, unit, and formula.
Magnetic Field Intensity

Magnetic field intensity definition-

The MMF for unit length (along the path of magnetic flux) is defined as the magnetic field intensity and it is designated by the symbol H. The magnetic field intensity thus can be expressed as-



H = Magnetomotive force / Mean length of the magnetic path
i.e. H =F/l = NI/l (AT/ m.)

where l is the mean length of the magnetic circuit in meters. Magnetic field intensity is also termed as magnetising force or magnetic field strength.

Magnetic field intensity formula -

magnetic field intensity formula

Unit of magnetic field intensity -

Unit of magnetic field intensity is AT/m that is Ampere Turn/meter.



More Detail - Magnetic field Wikipedia



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Magnetic Properties of Materials and Types of Magnetic Material

In This Post, we are going to discuss Magnetic Properties of Materials and Types of Magnetic Material, this topic will help you to understand magnetic materials

Magnetic Properties of Materials

Magnetic Properties of Materials
  • Magnetic materials are those materials within which a state of magnetization may be evoked.
  • The magnetic susceptibility depends on the nature of the magnetic material and its state, that is, temperature, etc.
  • The principal ferromagnetic elements are iron, cobalt, nickel.
  • The Curie-Weiss law states that


Magnetic Materials

where x = susceptibility, C = Curie temperature and Thita = paramagnetic Curie temperature.

  • When a ferromagnetic material is magnetized small changes in dimensions occur, the effect is known as "magnetostriction".
  • Diamagnetism is the property of material due to which it when placed in a magnetic field, becomes weakly magnetized in a direction opposite to the magnetization of the external fields. Practically all organic substances are diamagnetic.
  • The magnetic properties of all ferromagnetic materials depend upon their chemical composition, mechanical working and heat treatment. The general effect of impurities is to decrease the permeability and increase the hysteresis loss.
  • Permanent-magnet materials may be grouped into five classes as follows :
(i) Precipitation-hardened alloys
(ii) Quench-hardened alloys
(iii) Ceramic
(iv) Iron powder compacts
(v) Work-hardened materials.
  • Iron losses if allowed to take place unchecked, not only reduce the efficiency of electrical equipment but also raise the temperature of the core. Hence these losses should be kept as small as is economically possible.
  • Total iron loss is given by the relation
Magnetic Materials

where Pi = total iron loss, Ph = hysteresis loss, Pe = eddy current loss, Kh = hysteresis co-efficient, F = frequency, B(max) = maximum flux density, k = Steinmetz co-efficient and Ke = constant-eddy currents.


  • Magnetic hysteresis is defined as the lagging of magnetization or induction flux density (B) behind the magnetizing force (H) or it is that quality of a magnetic substance due to which energy is dissipated in it on the reversal of its magnetism.
  • Ageing of a permanent magnet is the process of normal or accelerated change, under continued normal or specified artificial conditions, in the strength of the magnetic field maintained. Metallurgical ageing is the result of a change in the metallurgical condition of the magnet, which changes its ability to remain in a magnetized condition.

Types of Magnetic Materials

1 - Diamagnetic materials
Diamagnetic materials are those that generally consider non-magnetic and include water, wood, most organic compounds such as petroleum and some plastics, and many metals, including copper, particularly heavy ones with many central electrons, such as mercury. , gold. and bismuth.


2 - Paramagnetic Materials
Materials that are called "Paramagnetic Materials" are those that exhibit, at least in an appreciable temperature range, magnetic susceptibilities that adhere to the Curie or Curie-Weiss laws. In principle, any system that contains atoms, ions or molecules with unpaired spins can be called a Paramagnetic Material, but the interactions between them must be carefully considered.


3 - Ferromagnetic Material
Ferromagnetic materials are those substances that exhibit a strong magnetism in the same direction of the field when a magnetic field is applied.


Must Read - Kirchhoff Law for Electrical Engineering
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Kirchhoff Law for Electrical Engineering

Kirchhoff Law for Electrical Engineering

For complex circuit computations, the following two laws first stated by Gutsav R. Kirchhoff (1824-1887) are indispensable.

Kirchhoff Law for Electrical Engineering


Kirchhoff's First Law (Point or Current Law)
The sum of the currents entering a junction is equal to the sum of the currents leaving the junction.

i.e., Sum of Currents entering = Sum of currents leaving.

Kirchhoff's Second Law (Mesh or Voltage Law)
The sum of e.m.f. (rise of potential) around any closed loop of a circuit equals the sum of the potential drops in that loop.

Considering a rise of potential as positive (+ ve) and a drop of potential as negative (-ve), the algebraic sum of potential differences (voltages) around a closed loop of a circuit is zero.

Sum of E - Sum of IR drops = 0 (around closed loop) i.e. Sum of E = Sum of  IR or Sum of Potential rises = Sum of potential drops

Applications of Kirchhoff s Laws

Kirchhoff's laws may be employed in the following methods of solving networks:
1. Branch-current method.
2. Maxwell's loop (or mesh) current method.
3. Nodal voltage method.

Also, SeeHow to Read Resistor Color Code

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How to Read Resistor Color Code

How to Read Resistor Color Code

  • Resistance is measured in units called ohms.
  • Wire wound resistors normally have their values in ohms and tolerance in percent stamped on them.
  • For carbon or composition resistors a color code is used.
The resistance values, for several years, have been coded by three colored bands painted around the body of the resistors. If the tolerance is either 5 or 10 percent, a fourth color bond is added. The position of the bands is shown below.


How to Read Resistor Color Code




  • The first two colors tell the first two digits in the resistance value.
  • The third band tells how many zeros follow the first two digits.
  • Sometimes a fourth band is present. This band tells the tolerance and will be either gold or silver. A gold band means 5% tolerance, silver 10%, and no fourth band, 20%. The tolerance band tells how close the resistance should be to the value shown by the other three bands.



The Producer of Reading the band is given below.



How to Read Resistor Color Code

The Blue-Red-Orange bands signify 62 followed by three zero and would be read as 62000 ohms +-20%.

Also SeeImportant Current Electricity Notes for Students

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Important Current Electricity Notes for Students

Important Current Electricity Notes

Today we are going to Provide you Current Electricity Notes like Electromotive Force, Resistance, Ohm's Law, Electrical Energy etc.

What is Electromotive Force?
Electromotive Force (E.M.F.) is the force that causes a current of electricity to flow. The Volte is the unit of potential difference and electromotive force.


Current Electricity Notes

What is Resistance in Electrical Engineering?
The Opposition to the flow of electron is called electrical Resistance. Resistance may also be defined as "The property of the electric circuit which opposes the flow of current". The Practical Unit of Electrical Resistance is ohm.

What is Ohm's Law?
"For a fixed metal conductor, the temperature and other conditions remaining constant, the current I through it is proportional to the potential difference V between its ends".

in other words, V/I = Constant or V/I = R, where R is the resistance of the conductor between the two points.

Also See - Top Electrical Engineering MCQ on Simple DC Networks

What is Electrical Energy?
Electrical Energy is expressed in terms of KW (kilowatt = 1000W) or MW (megawatt = 1000 KW)

1 kWh = 1 kw * 1 hour = 1000 watt-hours (=1000*60*60 watt-sec.)

What is Linear and Non-linear Resistor?
Linear Resistor - A Linear resistor is one which obeys Ohm's law. A circuit which contains only linear components is called a linear circuit.

Non-linear Resistor - Such elements in which the V/I (volt-ampere) plots are not straight lines but curves are called non-linear resistors or non-linear elements.


What is the Limitation of Ohm's Law?
Ohm's law does not apply under the following conditions:
1. Electrolytes where enormous gases are produced on either electrode.
2. Non-linear resistors like vacuum radio valves, semi-conductors, gas-filled tubes etc.
3. Arc lamps.
4. Metals which get heated up due to the flow of current through.
5. Appliances like metal rectifiers, crystal detectors, etc. in which operation depends on the direction of the current.

Classification of Resistors
The resistors 'are classified as follows:

1. Fixed resistors - The fixed resistor is the simplest type of resistor. Fixed means that the unit is so constructed that its resistance value is constant and unchangeable. These are made of a carbon composition and have a cover of black or brown hard plastics.

2. Tapped resistors - A tapped resistor is a resistor which has a tap, or connection, somewhere along the resistance material. These resistors are usually wire wound type. If they have more than one tap, they will have a separate terminal for each.

Also See - Top 24 Basic Electrical Engineering Questions with Answers

3. Variable resistors - A variable resistor has a movable contact that is used to adjust or select the resistance value between two or more terminals. A variable resistor is commonly called a control.


4. Special resistors - The most common type of special resistors is the fusible type. A fusible resistor has a definite resistance value and it protects the circuit much like a fuse. Another special resistor is the temperature compensating unit. Such resistors are used to provide special control of the circuit that must be extremely stable in their operation.

We hope that this post "Important Current Electricity Notes for Students" will help you in your preparation. if you have any suggestion and request, you can tell us through comment here.


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ElectricalNotes4u is a Blog for Electrical Engineering Students who want to learn Electrical Engineering online. We will Provide You Notes on all Major subject of electrical engineering. We also Provide Important MCQ that will help you to Prepare for Competitive Exam.