Module 3: Inductance and Inductor

Module 3: Electrical Fundamentals II, Topic 3.11: Inductance and Inductor

• Introduction: Students should be able to state Faraday's Law, describe voltage induction in moving conductors, induction principles, and the effects of magnetic field strength, flux change rate, and number of turns on induced voltage. They should also be able to describe mutual induction, and the effect of primary current and mutual inductance on induced voltage.

• Factors affecting mutual inductance: The number of turns in each coil, physical size, permeability, and positioning of coils relative to each other.

• Lenz's Law and polarity determination rules: The polarity of the induced EMF is such that the induced current creates a magnetic flux in the circuit that opposes the change causing it.

• Back EMF and self-induction: A voltage opposing the change in current is created by the magnetic field of the coil.

• Saturation point: When a material is magnetically saturated, no additional amount of external magnetization force will increase its internal level of magnetization. This means that increasing primary current will not increase induced EMF in the secondary.

• Principle uses of inductors: Radio antennas, induction stoves, and toroid chokes are examples.

• Basic Inductor Operation: The magnitude of the induced EMF in a circuit is proportional to the rate of change in magnetic flux. Faraday's law can be expressed as:

E = -N (ΔΦ / Δt)

where:

• E = Electromotive force (EMF)

• N = Number of turns

• ΔΦ = Rate of magnetic flux change

• Δt = Time interval

• Variations of Faraday's Law: In a changing magnetic field or a conductor moving in a static field, a voltage is induced in a coil of wire. The voltage generated is proportional to the speed of the coil entering/exiting the magnetic field.

• Lenz's Law: The induced current creates a magnetic field that opposes the change in the original magnetic field. The direction of the induced EMF/current is determined by Lenz's law. If the original magnetic field is increasing, the induced magnetic field opposes it and if the original field is decreasing, the induced field aids it.

• Magnetic Field of Current (Electromagnetism): A magnetic field exists when an electric current flows through a wire. The strength of the magnetic field is proportional to the current.

• Left-Hand Rule: The left-hand rule is used to determine the direction of a magnetic field around a conductor. Place your left hand around the conductor with your thumb pointing in the direction of the current, then your fingers will curl in the direction of the magnetic field.

• Electromagnetic Induction: Current switching on and off in a coil creates a changing magnetic field, which induces an EMF in a nearby conductor.

• Mutual Induction: Magnetic flux from one conductor induces an EMF in a nearby, electrically isolated conductor. Transformers utilize mutual inductance. Factors affecting mutual inductance include number of turns in each coil, physical size, permeability, and position of coils.

• Primary Current Affecting Induced Voltage: Increasing the primary current increases the magnetic field, which increases voltage in the secondary coil.

• Positioning of Coils: The amount of mutual inductance depends on the relative position of coils. Close coils have higher mutual inductance, and coils far apart have lower. Perpendicular coils have no mutual inductance.

• Mutual Inductance: Depends on the number of turns, physical size, permeability of each coil and position of coils relative to each other. Formula for Mutual inductance (M) is:

M = K√(L₁ x L₂)

where:

• K = Coefficient of coupling

• L₁ = Inductance of 1st coil

• L₂ = Inductance of 2nd coil

• Magnetic Saturation: When a material is magnetically saturated, no additional magnetization force will result in an increase of internal magnetization. Therefore, after magnetic saturation, increasing primary current will not increase the secondary induced EMF.

• Inductance: Opposes change in current. Characterized by a symbol L (Inductance). SI unit is the Henry (H). Used in circuit design to delay or block changes in current.

• Inductors: Components that oppose changes in current flow. Commonly also called chokes or reactors.

• Factors affecting coil inductance: Number of turns, diameter, length, core material, and number of layers.

• Coil Length: Longer lengths of coil, result in lower inductance.

• Core Material: The permeability of a material affects its reluctance to magnetic flux. High-permeability materials like soft iron, increase magnetic flux and boost inductance.

• Number of Coil Layers: Inductance is enhanced by winding coil in layers. More layers increase flux linkage.

• Series/Parallel Inductors: Series arrangement adds inductance values. Parallel arrangement results in lower equivalent inductance.

• Voltage/Current Relationship: Current lags voltage by 90 degrees in a purely inductive circuit.

• L/R Time Constant: The time required for current in an inductor to increase/decrease to 63.2% of its maximum value. Calculated as L/R. The maximum current flows after 5 time constants.

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This quiz focuses on Electrical Fundamentals II, specifically including the principles of inductance and inductors. Students will explore key concepts such as Faraday's Law, mutual and self-induction, and the factors affecting mutual inductance. Additionally, the quiz covers Lenz's Law and the saturation point in magnetic materials.