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The magnetic factor required to reduce the residual magnetization zero is called?

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Description : If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be?

Answer : If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be zero.

Answer : In D.C. machines the residual magnetism is of the order of 2 to 3 percent.

Description : ln HRC fuse the time between cut-off and final current zero is called

Answer : ln HRC fuse the time between cut-off and final current zero is called the arcing time

Description : Explain the “mitigation of power theft” and “faulty meter replacement” for energy conservation techniques to reduce commercial losses. 

Answer : Energy conservation techniques to reduce commercial losses:  1. Mitigation of Power Theft: Power theft being the most important issue which all of the service providing utilities ... agricultural sector. Prepaid meters may prove effective measures against unauthorized abstraction of energy. 

Description : An amplifier has a voltage gain of 120. To reduce distortion, 10% negative feedback is employed. The gain of the amplifier with feedback is  (1) 141 (2) 92.3 (3) 9.23 (4) 1.41

Answer : An amplifier has a voltage gain of 120. To reduce distortion, 10% negative feedback is employed. The gain of the amplifier with feedback is 9.23

Description : Why high voltage can reduce power loss?

Answer : when voltage has increased due to reduced current flow, thus power loss given by ( I^2R) will be low due to reduced current(I^2) provided that resistance (R) is constant.

Description : Which of the following has nearly zero temperature coefficient? A) Constantan B) Manganin C) Both A and B D) None of these

Answer : Which of the following has nearly zero temperature coefficient? A) Constantan B) Manganin C) Both A and B D) None of these

Description : Is electric potential zero when electric field is zero?

Answer : Yes  .If  electric  field  is  zero  then  electric  potential  is  zero  ,  not  even  one.

Description : Can the electric field between two positive charges be zero?

Answer : It  can  only  if  they  have  equal  charges.

Answer : A transformer can have regulation closer to zero on leading power factor.

Description : What is the value of capacitance required to improve power factor from 0.7 to 0.9. Given that: Real power = 50 W Vrms of the source = 120 Frequency = 50 Hz   #powerfactor

Description : What arc the errors occurring in measuring devices due to stray magnetic field and temp '? Explain how to compensate them.

Answer : 1. Error due to stray magnetic fields-   Main magnetic field gets disturbed by external magnetic fields known as stray magnetic fields.  2. Compensation technique   To avoid this error, ... resistance alloy having a negligible resistance temp coefficient in the ratio of 1:10 for pressure coil 

Description : Which of the following laws relates the magnetic field to the magnitude, direction, length, and proximity of the electric current? A) Lenz’s law B) Faraday’s law C) Biot–Savart law D) None of these

Answer : Which of the following laws relates the magnetic field to the magnitude, direction, length, and proximity of the electric current? A) Lenz’s law B) Faraday’s law C) Biot–Savart law D) None of these

Description : In a magnetic material hysteresis loss takes place primarily due to?

Answer : In a magnetic material hysteresis loss takes place primarily due to it high retentivity.

Description : An air gap is usually inserted in magnetic circuits to?

Answer : An air gap is usually inserted in magnetic circuits to prevent saturation.

Description : State the material used for making (1) Magnetic Core (2) Fuse element  

Answer : The material used for making of:  (1) Magnetic Core : Iron, cobalt, Nickel, CRGO, HRGO , silicon steel  (2) Fuse Element: Tin- lead wire, Tinned copper wire 

Description : Define magnetic permeability. State and explain the factors affecting permeability of magnetic materials

Answer : Permeability : The capability of the magnetic material to conduct the magnetic flux is known as permeability. Permeability and hysteresis loss are inversely related to each other. Factors ... impurities affect the geometric pattern of the crystals and are harmful to the magnetic property. 

Description : Explain magnetic effect employed in measuring instrument.

Answer : Magnetic Effect:  I) In PMMC meters:  ➢ When a current is passed through a conductor, magnetic field is produced round the conductor. Due to this field when current ... field it experiences a mechanical force.  Examples: Electrodynamometer type instruments, Induction type instrument. 

Description : Define the following terms: i) Magnetic flux density, ii) Reluctance, iii) Magneto-motive force, iv) Permeance.

Answer : (i) Magnetic flux density (B): It is the magnetic flux per unit area measured at right angles to the flux path. (Its unit is weber/m2 or tesla).  (ii) Reluctance: It is the ... flux to set up through it and it is reciprocal of reluctance. Permeance = 1/ Reluctance. Unit: weber/ampere.

Description : Derive an expression for energy stored in a magnetic field . 

Answer : Expression for energy stored in a magnetic field: The energy is stored in magnetic field when current increases and return back when the current decreases. At instant t' seconds after closer of switch ... energy absorbed by the magnetic field when current increases from 0 to I amperes 

Description : What is magnetic hysteresis? What is the cause of hysteresis?

Answer : Magnetic hysteresis: When a magnetic material is subjected to cycle of magnetization, it is found that flux density (B) in the material lags behind applied magnetizing force (H). This ... the movement of orientation, due to which the flux density lags behind the magnetic field intensity.

Description : Define magnetic lines of force. Also draw and show magnetic lines of force of a bar type magnet.

Answer : Magnetic Lines of force- These are the imaginary lines (having no physical existence) introduced by Faraday for the pictorial representation of the distribution of a magnetic field.  OR  A line of ... that the tangent at any point gives direction of the resultant force at that point. 

Description : Classify magnetic materials and explain in brief.

Answer : .embed-container { position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; max-width: 100%; } .embed-container iframe, .embed-container object, .embed-container embed { ... the absence of external magnetic field. Following are the ferromagnetic materials: Iron, Cobalt, Nickel.

Description : Compare electric and magnetic circuit.

Answer : Comparison between Magnetic and Electric Circuits

Description : Define magnetic circuit. Draw simple series magnetic circuit.

Description : Give the relation between magnetic field strength, magnetic flux density and permeability.

Description : Define magnetic flux density and state its formula.

Answer : The magnetic flux per unit area is called as magnetic flux density. Magnetic flux density is denoted by B. The formula for magnetic flux density is Weber per metre square or Tesla. Mathematically ... the unit of magnetic flux density is Weber per metre square which is also called as Tesla.

Description : Define magnetic field strength and state its unit.

Answer : Magnetic field strength is the force experienced by a unit N-pole when placed at any point in a magnetic field is known as magnetic field strength or magnetizing force. Magnetising force or magnetic field ... unit of length is metre. So the unit of magnetic field strength is ampere turns per metre.

Description : Define magnetic lines of force. Show the magnetic lines of force for bar type magnet.

Answer : Magnetic linens of force is the imaginary lines for magnetic field of magnet around it. These magnetic lines of forces are introduced by Michael Faraday. The direction of lines of force is from N-pole to S-pole. The figure shows lines of force for bar type magnet.

Description : The magnetic susceptibility of paramagnetic material is: A) Less than zero B) Less than one but positive C) Greater than one D) Equal to zero

Answer : The magnetic susceptibility of paramagnetic material is: Less than one but positive

Description : Magnetic circuit breakers use _________ A) Permanent magnets B) Earth magnets C) Solenoid D) All the above

Answer : Magnetic circuit breakers use Solenoid 

Description : Which of the following is a unit of magnetic flux? A) Weber B) Maxwell C) Both A and B D) None of these

Answer : Which of the following is a unit of magnetic flux? A) Weber B) Maxwell C) Both A and B D) None of these

Description : What is the SI unit for magnetic reluctance? A) Ampere B) Ampere-turns per weber C) Henry D) None of these

Answer : What is the SI unit for magnetic reluctance? A) Ampere B) Ampere-turns per weber C) Henry D) None of these

Description : The magnetic permeability of a diamagnet is _________ A) More than that of vacuum B) Same as that of vacuum C) Less than that of vacuum D) 3.14 times that of vacuum

Answer : The magnetic permeability of a diamagnet is Less than that of vacuum 

Description : The magnetic neutral plane shifts in a dc machine (A) in the direction of motion of motor (B) in the direction of motion of generator (C) due to increase in the field flux (D) cause reduction of flash over between commutator segments

Answer : The magnetic neutral plane shifts in a dc machine in the direction of motion of generator

Description : The property of a material which opposes the creation of magnetic flux in it is known as?

Answer : The property of a material which opposes the creation of magnetic flux in it is known as reluctance.

Description : A material for good magnetic memory should have?

Answer : A material for good magnetic memory should have high retentivity.

Description : Those magnetic materials are best suited for making armature and transformer cores which have____permeability and_______hystersis loss.

Answer : Those magnetic materials are best suited for making armature and transformer cores which have high permeability and low hystersis loss.

Description : Permeability in a magnetic circuit corresponds to______ in an electric circuit.

Answer : Permeability in a magnetic circuit corresponds to conductivity in an electric circuit.

Description : The unit of magnetic flux is?

Answer : The unit of magnetic flux is weber.

Answer : Yes, Induction heating is used for both magnetic and non-magnetic materials.

Description : The synchronous motor which works on leading power factor and does not drive any mechanical load is called?

Answer : The synchronous motor which works on leading power factor and does not drive any mechanical load is called synchronous condenser.

Description : The total magnetic moment  1. is called saturation magnetization.  2. depends on the number of magnetic dipoles per unit volume, the instant electric current and the area of the current loop.  Which of the above statements is/are correct ?

Answer : depends on the number of magnetic dipoles per unit volume, the instant electric current and the area of the current loop

Description : Why does the magnetic field flow from north to south?

Description : Why is it necessary to keep air gaps in magnetic circuits as small as possible?

Answer : To avoid the effect of stray magnetic field in A.C. bridges we can use magnetic screening.

Description : How can a magnetic field be used to generate an electric current?

Answer : Magnetic  field  can  be  used  to  generate  electric  current  on  a  condition  that  it  is  on  a  rate  of  changing  magnetic  flux.  (Faraday's  law)

Description : Explain hysteresis loss, eddy current loss and skin effect limitations with reference to magnetic material.

Answer : Hysteresis loss: Hysteresis loss is a loss which occurs due to the friction of magnetic domain due to the change in magnetic field in ferromagnetic material like iron. Hysteresis loss causes power loss ... loss in transformer is given by, We=Kef2Kf2Bm2watts Skin effect limitations:

Description : Magnetic and Non-magnetic Materials

Answer : We have now looked at a number of ways in which matter can be grouped, such as into metals, semi-metals and non-metals; electrical conductors and insulators, and thermal conductors and insulators. ... information must be stored, in computers and TV's, as well as in generators and electric motors.

Description : Electro Magnetic Induction

Answer : Electro Magnetic Induction

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