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

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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 

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69 views 1 answer
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)

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Answer :

Magnetic field in a D.C. generator is produced by electromagnets.

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129 views 1 answer
Description :

Why does the magnetic field flow from north to south?

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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

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67 views 1 answer
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 

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165 views 1 answer
Description :

A magnetic circuit has effective iron length of 100 cm and it is wound with 800 turns of wire carries 1 A. Find the magnetic field strength.

Answer :

magnetic field strength

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187 views 1 answer
Description :

Which of the following statements is not characteristic of a static magnetic field? (A) It is solenoidal. (B) It is conservative. (C) It has no sinks or sources. (D) Flux lines are always closed.

Answer :

Which of the following statements is not characteristic of a static magnetic field? (A) It is solenoidal. (B) It is conservative. (C) It has no sinks or sources. (D) Flux lines are always closed.

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1.6k views 1 answer
Description :

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

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69 views 0 answers
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.

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Description :

An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be  (1) unaffected (2) decreased (3) increased (4) either decreased or increased depending on the direction of the DC field

Answer :

An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be either decreased or increased depending on the direction of the DC field

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277 views 1 answer
Description :

Answer :

In a D.C. machine stray loss is the sum of iron loss and mechanical loss.

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111 views 1 answer
Description :

What is the percentage of stray losses in DC machine?

Answer :

Percentage of stray losses in DC machine is about 1 % .

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Description :

Answer :

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

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87 views 1 answer
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:

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582 views 1 answer
Description :

Define junction field effect transistor (JFET) and give an example.

Answer :

Junction Field-Effect Transistor: It is a semiconductor device having three terminals, namely Gate, Drain and Source, in which the current flow is controlled by an electric field set up by an external voltage applied ... : i) n-channel JFET and ii) p-channel JFET Examples of JFET: BFW 10, BFW 11 

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166 views 1 answer
Description :

Answer :

In a shaded pole single-phase motor, the revolving field is produced by the use of shading coils.

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91 views 1 answer
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. 

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81 views 1 answer
Description :

The effect of stray magnetic fields on the actuating torque of a portable instrument is maximum when the operating field of the instrument and the stray fields are  A) Perpendicular B) Parallel C) Inclined at 60" D) Inclined at 30°

Answer :

The effect of stray magnetic fields on the actuating torque of a portable instrument is maximum when the operating field of the instrument and the stray fields are Parallel 

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178 views 1 answer
Description :

Explain how in a 3 phase induction motor to a rotating magnetic field is developed. 

Answer :

Production of Rotating Magnetic Field in Three-phase Induction Motor: In three-phase induction motor, the three-phase stator windings are displaced in space by 120° and their three-phase currents are displaced ... time by 120°. Such fluxes give rise to the resultant rotating magnetic field.

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Description :

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

Answer :

Magnetic circuit breakers use Solenoid 

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Description :

A field of force can exist only between?

Answer :

A field of force can exist only between two ions.

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105 views 1 answer
Description :

Can the electric field between two positive charges be zero?

Answer :

It  can  only  if  they  have  equal  charges.

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Description :

Answer :

The stator of phase shifting transformer for use in conjunction with an A.C. potentiometer usually has a two-phase winding.

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131 views 1 answer
Description :

Why do we use AC current in our homes?

Answer :

We used it for cooking rice,  For washing clothes and for lights in the house.

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179 views 3 answers
Description :

Answer :

If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens this will make armature to take heavy current, possibly burning it.

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112 views 1 answer
Description :

Answer :

If the field of a D.C. shunt motor gets opened while motor is running the motor will attain dangerously high speed.

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108 views 1 answer
Description :

Answer :

Flashing the field of D.C. generator means creating residual magnetism by a D.C. source.

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66 views 1 answer
Description :

Can we apply the superposition theorem to AC circuit?

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Description :

Answer :

A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave will be of 5 Hz.

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140 views 1 answer
Description :

Answer :

In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when there is no load on|he generator.

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155 views 1 answer
Description :

The ability of materials to become polarized under an applied electric field is called _______ A) Ferroelectricity B) Paraelectricity C) Polectricity D) None of these

Answer :

The ability of materials to become polarized under an applied electric field is called Paraelectricity

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105 views 1 answer
Description :

It is possible to increase the field flux and, at the same time, increase the speed of a d.c. motor provided its .......... is held constant.

Answer :

It is possible to increase the field flux and, at the same time, increase the speed of a d.c. motor provided its armature current is held constant.

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80 views 1 answer
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.

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196 views 1 answer
Description :

Can we apply Norton's theorem in an AC circuit?

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76 views 0 answers
Description :

In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as  (1) synchronous motor (2) synchronous generator (3) asynchronous motor (4) asynchronous generator

Answer :

In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as synchronous generator 

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365 views 1 answer
Description :

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

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Description :

An air gap is usually inserted in magnetic circuits to?

Answer :

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

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81 views 1 answer
Description :

Energy stored in electrostatic field of capacitance formula

Answer :

Energy stored in electrostatic field of capacitance formula

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60 views 1 answer
Description :

An electric motor in which both stator field and rotor rotates with same speed is called?

Answer :

An electric motor in which both stator field and rotor rotates with same speed is called synchronous motor.

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107 views 1 answer
Description :

Briefly describe the electric field of a static charge.

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Description :

The electric field inside a hollow conducting sphere ________ A) Depends on the diameter of the sphere  B) Varies according to the direction of earth’s magnetic poles C) Is zero  D) None of these

Answer :

The electric field inside a hollow conducting sphere Is zero

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120 views 1 answer
Description :

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

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Description :

State advantages of rotating field type alternators. 

Answer :

Advantages of Rotating Field Type Alternator: 1) For high-voltage alternator, large space is required to accommodate conductors with insulation, as high voltage is induced in them. If field poles are placed ... is kept rotating. 8) Rotating field is comparatively light and can run with high speed. 

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Description :

 Field intensity formula

Answer :

 Field intensity formula

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Description :

Answer :

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will stop.

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127 views 1 answer
Description :

MOSFET uses the electric field of?

Answer :

MOSFET uses the electric field of gate capacitance.

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Description :

If the field of synchronous motor is under excited, power factor will be?

Answer :

If the field of synchronous motor is under excited, power factor will be lagging.

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219 views 1 answer
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.

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72 views 1 answer
Description :

What is the direction of the induced electric field?

Answer :

It  is  in  opposite  direction   to  the  one  that   produced  it.

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57 views 1 answer
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