NEIEP Magnetism and Electromagnetism (355)

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• In AC circuit analysis, RMS values represent which concept for power calculations?
• What is the typical brake clearance for geared machines?
• What is mutual induction and a practical example in power systems?
• Which statement about lines of magnetic force is best supported, according to the material?
• Which statement about leakage inductance is true?
• Overload relays used in elevators are self-resetting.
• Which flux component links both windings in a transformer core?
• How would you describe a coil and the effect of number of turns on inductance?
• What does the coupling coefficient k indicate in a transformer, and how does a low k affect performance?
• Which metal is used for the guard component in relay assemblies to prevent sticking?
• Which statement best describes the path of magnetic lines of force relative to poles?
• The magnetic field around a long straight conductor is directed how?
• In a series R-L-C circuit, how do the reactances X_L and X_C vary with frequency, and when does resonance occur?
• Why are ferrite cores preferred for high-frequency transformers?
• Which formula expresses the percent voltage regulation of a transformer?
• How does grounding of transformer neutrals affect fault currents and safety?
• What information does the B-H curve provide for magnetic materials?
• Does flux density increase or decrease as the distance from a magnet increases?
• In a pure resistor, what is the phase angle between voltage and current, and what is the power factor?
• What condition reduces eddy current losses in transformer cores?
• What is the role of a DC exciter in a synchronous generator?
• Describe the skin depth effect on AC resistance at high frequency.
• Mutual inductance M is related to self-inductances L1, L2 and coupling coefficient k by which expression?
• What type of magnet retains its magnetism after the outside magnetizing force is removed?
• A permanent magnet or reed switch will do what when a vane is next to it?
• In domain theory of magnetism, which statement is correct?
• Which statement correctly describes how generated EMF scales with flux and speed (assuming other factors constant)?
• How can you determine the direction of the magnetic field around a conductor?
• What happens when current flow exceeds the rating of a fuse in a circuit?
• Resonance in a series RLC circuit occurs when which condition is satisfied?
• Which core configuration is typically used to store energy in inductors?
• Which of the following is a typical permanent magnet application?
• Which statement about μ is correct?
• Which set of conditions yields maximum coupling in a transformer?
• In an ideal transformer, how are primary and secondary currents related to the turns ratio?
• What does the coupling coefficient k describe in transformer design?
• Which statement correctly describes the sign of the induced EMF according to Faraday's law?
• If N_p:N_s = 3:2 and Z_L = 25 Ω, what is Z_primary?
• What happens when power is applied to a coil?
• Which device is specifically used to limit inrush current by presenting high resistance when cold and decreasing as it heats?
• In a transformer with a wye connection, how does line voltage relate to phase voltage?
• Which of the following are listed as ways permanent magnets can be damaged?
• What is the magnetic flux linkage in a coil with N turns carrying flux Φ?
• Which particles' spin determines the direction of a magnetic field?
• In a wye-connected transformer, how does line current relate to phase current?
• If the commutator fails to reverse current direction each half-cycle, what happens to motor torque?
• Laminations in magnetic cores primarily reduce which losses?
• For a long straight wire carrying current I, which expression gives the magnetic flux density B at distance r from the wire?
• What does permeability describe in magnetic materials?
• In a DC generator, which factors determine the generated EMF according to the emf equation?
• How does frequency affect hysteresis loss in a transformer core?
• The laminated magnetic core in transformers is primarily used to reduce which loss mechanism?
• For a long straight conductor carrying current I, which expression gives the magnetic field at distance r?
• Lines of force are a lot like what?
• Flux linkage is defined as which expression?
• What is the typical brake clearance for gearless machines?
• Reactive power expression.
• For a uniform magnetic flux density B perpendicular to a surface of area A, the magnetic flux Φ is equal to
• Which statement describes the right-hand rule for determining the direction of the magnetic field around a straight current-carrying conductor?
• Inside an ideal long solenoid, the magnetic field is:
• What effect does inserting a gap in a magnetic core have for an energy-storage inductor?
• The concentration of magnetic flux lines within a material after packing according to its permeability is called what?
• What is the main reason AC machines experience core losses and how are these mitigated in design?
• When a relay coil is energized, which property of the flux lines combines to pull the armature against the frame?
• Explain the difference between leakage flux and main flux in a transformer core.
• In a simple magnetic circuit, flux is determined by the magnetomotive force NI and reluctance; for a fixed reluctance, what happens when NI increases?
• What is the purpose of a tap changer in a transformer?
• Which scenario is listed as a damage mechanism for permanent magnets?
• What is the typical brake clearance for geared machines and for gearless machines?
• In the EMF equation E_phase = 4.44 f N Φ_m, what does Φ_m represent?
• What information does a B-H curve provide for a magnetic material?
• Why is it important to limit inrush current when energizing transformer primary or inductive loads and how is it controlled?
• Between Alnico 5 and Alnico 6, which material has the higher retentivity?
• In AC circuit analysis, a phasor is used primarily to simplify calculations by representing voltage or current as what?
• Magnetic field strength is directly proportional to what?
• After a fuse melts, what should be done to restore the circuit?
• Do like poles repel and unlike poles attract?
• Which analogy best describes lines of magnetic force as described in the material?
• What is the phasor representation of AC quantities and how are RMS values defined for sine waves?
• Which statement about magnetic reluctance is true?
• Which equation expresses the generated EMF of a DC generator as a function of speed, number of poles, and flux per pole?
• What is it called when a closed loop of magnetic lines from the north pole to the south pole outside of a magnet and from the south pole to the north pole inside of a magnet?
• Which type of switch is activated by the presence of a magnetic field and is commonly used for sensing without direct contact?
• Magnetic flux density B relates to the magnetic permeability μ and magnetic field H by which equation?
• For a series R-L-C circuit, impedance is Z = R + j(ω L − 1/(ω C)). When does resonance occur?
• The amount of magnetic force remaining after the magnetizing force is removed is called what?
• What is the correct expression for inductive reactance and how does it change with frequency?
• Lines of magnetic force are called what?
• Which instrument can measure current in a circuit without disconnecting any components?
• What is the movable part of a relay called?
• In an AC motor, three-phase power creates what that induces rotor current?
• For two windings with nominal coupling, what is the value of the coupling coefficient k in a perfectly coupled transformer?
• What is residual flux density Br and why is it important for permanent magnets?
• Define flux linkage and its relationship to inductance.
• What is the accepted value of the permeability of free space μ0?
• What does a circuit breaker do when current flow exceeds its rated level?
• As H increases into saturation, what happens to B?
• If the secondary turns Ns are greater than primary turns Np in an ideal transformer, Vs is relative to Vp how?
• In an ideal transformer, how are input and output powers related?
• Where does the 4.44 factor in the EMF equation for sinusoidal excitation originate?
• If current flow increases, what happens to the magnetic field?
• Name the two main core losses in AC machines and their causes.
• Write the phasor impedance for resistor, inductor, and capacitor, and give X_L and X_C.
• Which set of equations correctly describes the voltages in two coupled coils with self-inductances L1, L2 and mutual inductance M?
• What is the purpose of a residual guard or brass pad in a relay?
• Why are laminated cores used in transformers and electrical machines?
• What happens to elevator brakes when power is removed?
• What statement is correct about relays?
• Which statement about lines of magnetic force is false?
• What is the magnetizing force in an electromagnet?
• What is the reflected impedance to the primary Z_ref in terms of turns ratio and load Z_load?
• What is the effect of increasing load on transformer regulation?
• For a uniform magnetic field B passing perpendicularly through an area A, the magnetic flux Φ is equal to:
• What is it called when magnetism is produced by the flow of an electric current?
• The slope of the B-H curve in the initial linear region represents which property of the material?
• Which statement describes how flux lines behave when a coil is energized around a ferrous core?
• Which statement correctly distinguishes mutual inductance from transformer coupling?
• If a transformer has turns ratio N_p:N_s = 2:1 and the secondary load Z_L = 15 Ω, what is Z_primary?
• Which statement about magnetic flux lines is correct?
• What is a phasor and how is it used in AC circuit analysis?
• Which term is used to describe retentivity, or the ability to hold magnetization?
• What is the typical unit for inductance and its relation to flux and current?
• Which statement best describes the right-hand rule for the direction of the magnetic field around a straight current-carrying wire?
• Pure annealed iron has a relative permeability of approximately between which values?
• In an ideal transformer, which statement is true about the voltage and turns?
• The reluctance Rm of a uniform magnetic path with length l, cross-sectional area A, and permeability μ is given by which expression?
• Which expression correctly defines magnetic reluctance Rm?
• In a purely resistive, inductive, and capacitive AC circuit, how does current relate to voltage?
• In an AC machine, what is synchronism in the context of synchronous generators?
• In a magnetic system with two coupled inductors, which expression gives the energy stored?
• What is the magnetic energy density in a linear material in terms of B and μ?
• Which property primarily determines hysteresis loss in a transformer core?
• The transformer coupling coefficient k is defined as M / sqrt(L1 L2). Which statement is true?
• Does an electromagnetic field persist if no current is flowing?
• What factors influence transformer short-circuit current and how is it related to leakage inductance?
• Which protective device opens the circuit by melting when current exceeds its rating?
• Which expression represents Faraday's law for induced emf due to a changing magnetic flux?
• The ease with which magnetic lines of force distribute themselves throughout a material is referred to as what?
• The magnitude of the impedance in a series RLC circuit is given by which expression?
• Define flux in the magnetic circuit context and state its unit.
• What is the SI unit of magnetic flux?
• No-load current in a transformer is primarily:
• Which description correctly explains the left-hand rule?
• How does the magnetizing current relate to core flux and reflected load in a transformer?
• What is the unit of inductive reactance X_L?
• Which statement correctly describes lines of magnetic force extending from a magnet?
• What is the term for when groups of atoms align their magnetic fields in a common direction?
• The power factor in an AC circuit is defined as which and what is its behavior with inductive or capacitive loads?
• What type of switch is momentary contact and only changes state while in presence of a magnetic field, then returns to previous state when away from magnet?
• In a relay, which part is stationary and provides the magnetic path?
• What is the term used for the degree to which a magnetic force can be established in a material?
• Inductive reactance X_L of an inductor with inductance L at frequency f is:
• What does coercivity represent on the B-H curve?
• Explain the operation principle of a DC motor and the role of the commutator.
• Which statement best distinguishes mutual inductance M from leakage inductance?
• In a coil, what happens to inductance as the operating flux density approaches saturation?
• Inserting a small air gap in a magnetic circuit affects flux: which statement is correct?
• How does an AC electric motor rotate?
• How does a transformer with gapped vs ungapped core differ in terms of energy transformation?
• Which pole is associated with the starting point of magnetic lines of force outside a magnet?
• What is voltage regulation in a transformer?
• Which of the following best describes lines of force around a magnet?
• Which statement correctly describes core loss dependencies on frequency and flux density?
• Describe the effect of distributed windings on leakage inductance.
• Hysteresis losses in transformer cores arise from what, whereas eddy current losses arise from what?
• In the left-hand rule explanation, which part indicates magnetic field direction around the conductor?
• Capacitive reactance X_C of a capacitor C at frequency f is:
• What design feature in relays helps ensure they release when de-energized?
• Why should you have a ceramic permanent magnet on an escalator brake?
• What is the name of the modern theory of magnetism based on electron spin?
• What is the energy stored in a single inductor as a function of inductance and current?
• Why are transformer cores laminated?
• What is a common example of a solenoid?
• Which of the following is an example of a permanent magnet application?
• How do you adjust the air gap between the armature and frame when the relay is dropped out?
• Which statement is true about magnetic circuits?
• Which statement correctly describes the left-hand rule for determining the magnetic field around a current-carrying conductor?
• Magnetic flux Φ through a surface is defined as:
• What type of switch has an on and off state and maintains contact until it is actuated by passing in close proximity to a magnetic field?
• The induced EMF in a coil with N turns is given by which expression?
• Which type of switch uses vanes?
• Laminations reduce eddy current losses by
• In a series RLC circuit at resonance, what happens to the reactive components and the impedance?
• Which equation correctly expresses the induced electromotive force (EMF) in a coil with N turns due to a changing magnetic flux Φ?
• Magnets created by the flow of electricity are called what?
• What is the expression for the energy stored in an inductor and how does it depend on current?
• Which term describes a closed loop of magnetic flux that forms part of the magnetic circuit?
• Outside a magnet, in which direction do the magnetic lines of force travel?
• How would you calculate the percentage efficiency of a transformer given input power and output power?
• In magnetic hysteresis, the area of the B-H loop per cycle represents which of the following?
• If you increase the inductance of a single inductor while keeping current constant, what happens to the stored energy?
• Which design choice reduces eddy current losses in a transformer core?
• In a transformer core, what effect does adding an air gap have on inductance and leakage inductance?
• If the magnetic flux through a coil changes with time, how does the induced EMF vary with the number of turns?
• What causes the secondary voltage to drop when a transformer is loaded?
• Which term describes the alignment of atomic magnetic fields in a material that results in macroscopic magnetization?
• What is the primary mechanism by which a transformer transfers energy between windings?
• Total magnetic flux Φ in terms of the MMF F and reluctance Rm is which relation?
• Which statement about lines of force and poles is correct?
• What describes the maximum magnetization under an applied field?
• What can you use to ensure the relay armature will drop out when de-energized?
• An ideal transformer is characterized by which properties?
• In a linear, isotropic magnetic material, the magnetic flux density B is related to the magnetic field strength H by which relation?
• Where do magnetic lines of force originate relative to the magnet's poles?
• What is the magnetomotive force (MMF) in a magnetic circuit?
• Power factor is defined as cos φ, where φ is the phase angle between voltage and current. What is PF when φ = 0?
• The direction of the magnetic field is determined by the spin of which particles?
• Is it acceptable to use a cracked permanent magnet?
• For a generator with sinusoidal flux linkage, the generated EMF per phase is approximately given by which expression?
• The term for the material's ability to retain magnetism is which?
• In a series RLC circuit, the impedance Z is expressed as which of the following?
• Which flux component does not couple to the other winding and flows outside the intended magnetic path?
• What instrument would you use to measure the DC resistance of windings and the insulation resistance of cables, and what do these measurements indicate?
• What is the effect of increasing frequency on transformer magnetizing current and core losses?
• What material are permanent magnets used on escalators and moving walks made of?
• Which of the following describes the maximum magnetization a material can achieve under an external field?
• Which expression correctly gives the energy density in a linear magnetic material in terms of H?
• The total flux linkage in a coil with N turns is equal to which quantity?
• How do permeability and magnetic saturation affect the B-H curve and inductance?
• Which term describes the magnet's memory of its previous magnetization?
• What is the role of ampere-turns in determining flux in a magnetic circuit?
• Describe skin depth and its impact on conductor resistance at high frequency.
• What do lines of force tend to do when stretched?
• Why does a transformer require an alternating current (AC) input rather than direct current (DC)?
• A coil of wire wound along a core of uniform diameter is called what?
• True or false, lines of magnetic force can cross each other?
• What feature between the armature and core of a relay helps it drop out when not energized?
• Synchronous speed of a four-pole machine at 60 Hz is what value in rpm?
• Which statement correctly describes how to reduce both hysteresis loss and eddy current loss in magnetic cores?
• What are the two main core losses in transformers?
• Inductance L relates flux linkage λ to current I by which expression?
• Which expression correctly relates induced EMF to flux linkage in a coil?
• Which expressions define inductance L and its relation to the induced emf e and changing current I?
• Which statement describes a solenoid?
• In AC circuits, real power P, reactive power Q, and apparent power S are defined by which formulas?
• How does a phase difference between voltage and current affect real and reactive power flow?
• Which description best describes the magnetic circuit concept?
• What is it called when a small magnet will pick up iron and steel objects or even another magnet?
• Inside a long solenoid with N turns and length l carrying current I, the magnetic field is?