Magnetic Circuits and Transformers

According to Ampere's law, what is the line integral of the magnetic field intensity H around a closed path equal to?

A straight wire 1 meter long carries a current of 10 A perpendicular to a magnetic field of B = 0.5 T. What is the magnitude of the force on the wire?

In the context of magnetic circuits, what is the term for the quantity analogous to resistance in an electrical circuit?

What is the primary reason for using laminated iron cores in transformers and motors operating with AC?

An ideal transformer has a voltage stepped up from the primary to the secondary. What happens to the current?

A 10-turn circular coil has a radius of 5 cm. A flux density of 0.5 T is directed perpendicular to the plane of the coil. What are the total flux linkages?

In a real transformer's equivalent circuit, what does the magnetizing inductance Lm account for?

An ideal transformer is used to connect a 50 ohm resistive load to a source. If the turns ratio N1/N2 is 10, what is the impedance seen by the source?

What is Lenz's law?

A 500-turn coil is wound on a magnetic core with a reluctance of 4.6 x 10^6 A-turns/Wb. What is the inductance of the coil?

What does the dot convention in a circuit diagram for mutually coupled coils indicate?

For a material with a B-H curve, what is the term for the flux density that remains in the core when the applied field H is reduced to zero from saturation?

The power loss due to eddy currents in a transformer core is proportional to what power of the frequency, assuming a given peak flux density?

Two coils are wound on a toroidal core with a reluctance of 10^7 ampere-turns/Wb. Coil 1 has 100 turns and Coil 2 has 200 turns. What is the self-inductance of Coil 2?

A toroidal core has a relative permeability of 6000, a mean length of 23.5 cm, and a cross-sectional area of 6 x 10^-4 m^2. Calculate the reluctance of the core. The permeability of free space is 4pi x 10^-7 Wb/Am.

For a toroidal coil, the magnetomotive force (mmf) is given by F = NI. The magnetic flux is given by Φ = F/R. Which formula correctly expresses the flux Φ in terms of N, I, core permeability µ, core radius r, and mean path radius R?

What is the consequence on transformer regulation and efficiency if the equivalent circuit includes elements like winding resistance (R1, R2) and leakage reactance (L1, L2)?

A 4700-V-rms ac source is used with a transformer to deliver 220 V rms to a load. What is the required turns ratio N1/N2 for this ideal transformer?

What is the relationship between the magnetic flux density (B) and the magnetic field intensity (H)?

An ideal transformer has a primary current I1rms and a secondary current I2rms, with turns N1 and N2 respectively. Which equation correctly relates the currents?

The area of the hysteresis loop on a B-H plot for a magnetic material represents what physical quantity?

Two coils are wound on a common core with L1 = 6.667 mH, L2 = 60 mH, and M = 10 mH. If a dot is placed on the top end of coil 1, where should the dot be placed on coil 2 if currents entering the dots are to produce aiding fluxes in paths 1 and 2 of the core shown in Figure 14.17?

What is the definition of percentage regulation for a transformer?

A toroidal core has N turns, current I, and mean path length l = 2piR. What is the magnetic field intensity H on the center line of the core?

In a magnetic circuit with an iron core and a substantial air gap, where does nearly all of the stored energy reside?

What is the primary power advantage of using high-voltage transmission lines for distributing electrical power over long distances?

An electron with charge q = -1.602 x 10^-19 C travels at 10^5 m/s in the positive x direction. The magnetic flux density is 1 T in the positive y direction. What is the force on the electron?

What physical principle is demonstrated by a conductor moving on rails through a magnetic field, where the induced voltage (e = Blu) leads to a force (f = iAlB) that accelerates the bar?

For a material with relative permeability mr = 5000, what is its absolute permeability µ? The permeability of free space is µ0 = 4pi x 10^-7 Wb/Am.

What is the primary function of an ideal transformer in an electrical circuit?

A long straight wire surrounded by air carries a current of 20 A. What is the magnetic flux density B at a point 1 cm from the wire? (Use µ0 = 4pi x 10^-7 Wb/Am)

What is the mechanical analog of an electrical transformer, as described in the text?

The reluctance of an iron path is 5.195 x 10^4 A-turns/Wb and the reluctance of an air gap in series is 4.547 x 10^6 A-turns/Wb. What is the total reluctance?

Why is the starting current of an ideal transformer with an open secondary switch equal to zero?

What is the primary cause of core loss in a magnetic material subjected to an AC current?

A magnetic circuit has a coil of 500 turns carrying a current of 2.012 A. What is the magnetomotive force (mmf)?

For which type of material would a designer choose a B-H curve with a large residual field and a wide hysteresis loop?

An ideal transformer reflects a load impedance ZL to the primary side as Z'L. What is the relationship between Z'L and ZL if the primary has N1 turns and the secondary has N2 turns?

A conductor of length 0.2 m moves at a velocity of 12 m/s, cutting through a perpendicular magnetic field of 0.5 T. What is the voltage induced across the ends of the conductor?

How is the magnetic flux (Φ) passing through a surface area A generally defined?

In the magnetic circuit analogies, magnetomotive force (F = Ni) is the analog of what quantity in an electrical circuit?

What is the phenomenon called 'fringing' in a magnetic circuit with an air gap?

Two parallel wires are 10 cm apart, and a 1-m length of the wires experience a repulsive force of 2 x 10^-4 N. What can be concluded about the currents in the wires?

The inductance of a 200-turn coil is 400 mH. If the number of turns is increased to 400, and all other properties of the magnetic circuit remain the same, what is the new inductance?

In an ideal transformer, the total mmf applied to the core is F = N1i1(t) - N2i2(t). Why is this total mmf considered to be zero?

What is the relationship between the developed power (Pdev), the air-gap power (Pag), and the slip (s) in an induction motor?

Which statement correctly describes the self inductances L1 and L2 and the mutual inductance M of two coils?

A magnetic circuit has a path length 'l', cross-sectional area 'A', and permeability 'µ'. What is the formula for its reluctance 'R'?

What is the key assumption about an ideal transformer's power efficiency?

The energy W delivered to a coil with N turns and zero resistance is given by the integral of Ni dΦ. If Ni = Hl and dΦ = AdB, where l is the mean path length and A is the cross-sectional area, what is the resulting expression for energy per unit volume, Wv?