# 600+ Electromagnetics Solved MCQs

55
56.5k
401.

## The unit of retentivity is

A. weber
B. weber/sq. m
C. ampere turn/metre
D. ampere turn
402.

## Reciprocal of reluctance is

A. reluctivity
B. permeance
C. permeability
D. susceptibility
403.

A. metre/henry
B. henry/metre
C. henry
D. 1/henry
404.

## A ferrite core has less eddy current loss than an iron core because

A. ferrites have high resistance
B. ferrites are magnetic
C. ferrites have low permeability
D. ferrites have high hysteresis
Answer» D. ferrites have high hysteresis
405.

## Hysteresis loss least depends on

A. volume of material
B. frequency
C. steinmetz co-efficient of material
D. ambient temperature
406.

## Laminated cores, in electrical machines, are used to reduce

A. copper loss
B. eddy current loss
C. hysteresis loss
D. all of the above
407.

## The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as

A. self-inductance
B. mutual inductance
C. series aiding inductance
D. capacitance
408.

## Which of the following circuit element stores energy in the electromagnetic field ?

A. inductance
B. condenser
C. variable resistor
D. resistance
409.

## Higher the self-inductance of a coil,

A. lesser its weber-turns
B. lower the e.m.f. induced
C. greater the flux produced by it
D. longer the delay in establishing steady current through it
410.

## In an iron cored coil the iron core is removed so that the coil becomes an air cored coil. The inductance of the coil will

A. increase
B. decrease
C. remain the same
D. initially increase and then decrease
411.

A. unaffected
B. doubled
C. halved
412.

## If current in a conductor increases then according to Lenz's law self-induced voltage will

A. aid the increasing current
B. tend to decrease the amount of cur-rent
C. produce current opposite to the in-creasing current
D. aid the applied voltage
Answer» C. produce current opposite to the in-creasing current
413.

## The direction of incViced e.m.f. can be found by

A. laplace\s law
B. lenz\s law
C. fleming\s right hand rule
D. kirchhoff s voltage law
414.

## Air-core coils are practically free from

A. hysteresis losses
B. eddy current losses
C. both (a) and (b)
D. none of the above
Answer» C. both (a) and (b)
415.

## The magnitude of the induced e.m.f. in a conductor depends on the

A. flux density of the magnetic field
B. amount of flux cut
D. rate of change of flux-linkages
416.

## Mutually inductance between two magnetically-coupled coils depends on

A. permeability of the core
B. the number of their turns
C. cross-sectional area of their com-mon core
D. all of the above
Answer» D. all of the above
417.

## A laminated iron core has reduced eddy-current losses because

A. more wire can be used with less d.c. resistance in coil
B. the laminations are insulated from each other
C. the magnetic flux is concentrated in the air gap of the core
D. the laminations are stacked vertf-cally
Answer» B. the laminations are insulated from each other
418.

B. lenz
C. newton
D. coulomb
419.

## Which of the following is not a unit of inductance ?

A. henry
B. coulomb/volt ampere
C. volt second per ampere
D. all of the above
420.

## In case of an inductance, current is proportional to

A. voltage across the inductance
B. magnetic field
C. both (a) and (b)
D. neither (a) nor (b)
421.

## Which of the following circuit elements will oppose the change in circuit current ?

A. capacitance
B. inductance
C. resistance
D. all of the above
422.

## For a purely inductive circuit which of the following is true ?

A. apparent power is zero
B. relative power is.zero
C. actual power of the circuit is zero
D. any capacitance even if present in the circuit will not be charged
Answer» C. actual power of the circuit is zero
423.

A. ohm
B. henry
C. ampere turns
D. webers/metre
424.

A. 64 a/s
B. 32 a/s
C. 16 a/s
D. 4 a/s
425.

A. 4 mh
B. 5 mh
C. 6 mh
D. 12 mh
426.

A. 32 mh
B. 38 mh
C. 40 mh
D. 48 mh
427.

A. 6 mh
B. 14 mh
C. 24 mh
D. 48 mh
428.

A. 6 h
B. 8 h
C. 12 h
D. 24 h
429.

A. 2.0
B. 1.0
C. 0.5
D. zero
430.

A. 50 ohms
B. 500 ohms
C. 1000 ohms
D. 5000 ohms
431.

## Lenz's law is a consequence of the law of conservation of

A. induced current
B. charge
C. energy
D. induced e.m.f.
432.

A. 50 n
B. 120 n
C. 240 n
D. 480 n
433.

A. 100 n
B. 400 n
C. 600 n
D. 1000 n
434.

## The co-efficient of coupling between two air core coils depends on

A. self-inductance of two coils only
B. mutual inductance between two coils only
C. mutual inductance and self inductance of two coils
D. none of the above
Answer» C. mutual inductance and self inductance of two coils
435.

A. 20 wb
B. 2 wb
C. 0.2 wb
D. 0.02 wb
436.

A. 0.01 s
B. 0.1 s
C. 0.5 s
D. 5 s
437.

## Which of the fpllowing inductor will have the least eddy current losses ?

A. air core
B. laminated iron core
C. iron core
D. powdered iron core
438.

A. 3500 mh
B. 350 mh
C. 250 mh
D. 150 mh
439.

A. 300 uh
B. 600 uh
C. 150 uh
D. 75 uh
440.

A. 5 mh
B. 10 mh
C. 5 h
D. 10 h
441.

## Which circuit element(s) will oppose the change in circuit current ?

A. resistance only
B. inductance only
C. capacitance only
D. inductance and capacitance
442.

## A crack in the magnetic path of an inductor will result in

A. unchanged inductance
B. increased inductance
C. zero inductance
D. reduced inductance
443.

## A coil is wound on iron core which carries current I. The self-induced voltage in the coil is not affected by

A. variation in coil current
B. variation in voltage to the coil
C. change of number of turns of coil
D. the resistance of magnetic path
Answer» B. variation in voltage to the coil
444.

## Which of the following parameters is not a primary parameter?

A. resistance
B. attenuation constant
C. capacitance
D. conductance
445.

A. lumped
B. distributed
C. parallel
D. paired
446.

A. lumped
B. distributed
C. parallel
D. paired
447.

A. g
B. c
C. l
D. r
448.

A. r
B. l
C. c
D. g
449.

A. g
B. r
C. c
D. l
450.

A. 25.2
B. 22.8
C. 28.8
D. 20
451.

A. 25
B. 1.33
C. 7
D. 0.75
452.

A. zo = √(lc)
B. zo = lc
C. zo = √(l/c)
D. zo = l/c
453.

A. parallel
B. perpendicular
C. polarized
D. matched
454.

A. 2
B. 1
C. 0.5
D. 3.14
455.

A. 50
B. 5
C. 0.5
D. 0.05
456.

A. 2
B. 3.14
C. 6.28
D. 1
457.

A. 0.75 ghz
B. 0.133 ghz
C. 7.5 ghz
D. 1.33 ghz
458.

A. v = ω/β
B. v = ωβ
C. v = β/ω
D. vωβ = 1
459.

## The electrical length in a transmission line refers to the

A. product of attenuation constant and length
B. ratio of attenuation constant and length
C. product of phase constant and length
D. ratio of phase constant and length
Answer» A. product of attenuation constant and length
460.

A. decibel
B. bel
C. neper
D. no unit
461.

A. 2 – 3j
B. 3 – 2j
C. 2 + 3j
D. 3 + 2j
462.

A. 1 x 108
B. 1.5 x 108
C. 3 x 108
D. 1 x 109
463.

## Identify the secondary parameter from the options given below.

A. resistance
B. conductance
C. phase constant
D. capacitance
464.

## Which of the following parameters does not exist in the transmission line equation?

A. r
B. zo
C. zl
D. propagation constant
465.

A. 25
B. 100
C. 2500
D. 50
466.

A. l = λ/4
B. l = λ/8
C. l = λ/2
D. l = ∞
467.

A. zin = zo
B. z = zo
C. zl = zo
D. zin = zl
468.

A. 25
B. 50
C. 6.25
D. 12.5
469.

## The condition for a quarter wave transformer is

A. zo2 = zin zl
B. zo = zin zl
C. zl2 = zin zo
D. zo = zin
Answer» A. zo2 = zin zl
470.

A. 50
B. 25
C. 75
D. 35.35
471.

A. 28.125
B. 12.285
C. 52.185
D. 85.128
472.

A. 1
B. -1
C. 0
D.
473.

## The purpose of the transmission line equation is to

A. find primary parameters
B. find secondary parameters
C. find the reflection cofficient
D. impedance matching
474.

## The quarter wave transformer can be considered as a

A. impedance inverter
B. impedance doubler
C. impedance tripler
475.

A. l = λ
B. l = λ/2
C. l = λ/4
D. l = λ/8
476.

A. 47.43
B. 37.34
C. 73.23
D. 67.45
477.

A. 50
B. 20
C. 1000
D. 125
478.

## The reflection coefficient lies in the range of

A. 0 < τ < 1
B. -1 < τ < 1
C. 1 < τ < ∞
D. 0 < τ < ∞
Answer» A. 0 < τ < 1
479.

A. 1/5
B. 5
C. 10
D. 25
480.

A. 1.35
B. 0.65
C. 0.35
D. 0.7
481.

A. 14.4
B. 16.6
C. 13.3
D. 11.1
482.

A. 0.5
B. 1
C. 0.38
D. 0.1
483.

A. 0
B. 0.5
C. 0.25
D. 0.2
484.

A. 17
B. 3
C. 10/7
D. 0.7
485.

A. 0.389
B. 0.55
C. 0.133
D. 0.42
486.

A. 1/4
B. 3/2
C. 3/4
D. 2/3
487.

A. 1/4
B. 1/8
C. 1/2
D. 3/4
488.

A. 0
B. 1
C. -1
D. infinity
489.

## Standing waves occurs due to

A. impedance match
B. impedance mismatch
C. reflection
D. transmission
490.

## Standing wave ratio is defined as the

A. ratio of voltage maxima to voltage minima
B. ratio of current maxima to current minima
C. product of voltage maxima and voltage minima
D. product of current maxima and current minima
Answer» A. ratio of voltage maxima to voltage minima
491.

A. 2
B. 4
C. 6
D. 8
492.

A. 2
B. 3
C. 1/2
D. 4
493.

A. 0.3
B. 75
C. 250
D. 3.33
494.

A. 0.55
B. 0.23
C. 0.48
D. 0.68
495.

## The range of the standing wave ratio is

A. 0 < s < 1
B. -1 < s < 1
C. 1 < s < ∞
D. 0 < s < ∞
Answer» C. 1 < s < ∞
496.

A. 0
B.
C. -1
D. 1
497.

A. 50/3
B. 3/50
C. 150
D. 450
498.

A. 100
B. 50
C. 25
D. 30
499.

A. 0
B. 1
C. -1
D.
500.

A. 0
B. 0.65
C. -0.65
D. 0.35