290+ Electromagnetic Theory Solved MCQs

Chapters

35
53.9k
Chapter: Electrostatics
101.

C. Weber/metre
D. Weber/sq-m
102.

Dielectric strength of a material depends on

A. moisture content
B. temperature
C. thickness
D. all of the above
Answer» D. all of the above
103.

What will happen to an insulating medium if voltage more than the breakdown voltage is applied on it ?

A. It will become magnetic
B. It will melt
C. It will get punctured or cracked
D. Its molecular structure will get changed
Answer» C. It will get punctured or cracked
104.

A. Paraffin wax
B. Quartz
C. Glass
D. Air
105.

1 volt/metre is same as

A. 1 metre/coulomb
B. 1 newton metre
C. 1 newton/metre
D. 1 joule/coulomb
106.

One volt is the same as

A. one joule/coulomb
B. one coulomb/joule
C. one coulomb
D. one joule
107.

The capacitance between two plates increases with

A. shorter plate area and higher ap¬plied voltage
B. shorter plate area and shorter dis¬tance between them
C. larger plate area, longer distance between plates and higher,applied voltage
D. larger plate area and shorter distance between plates
Answer» D. larger plate area and shorter distance between plates
108.

A. CIR
B. 1/RC
C. RC
D. RIC
109.

The bridge used for the measurement of the value of the capacitance is

A. Wien's bridge
B. Wheatstone bridge
C. Schering bridge
D. Hay's bridge
110.

If an ohmmeter reading immediately goes practically to zero and stays there, capacitor is

A. charged
B. short-circuited
C. lossy
D. satisfactory
111.

Out of the following capacitors of identical rating which one will have the smallest dimensions ?

A. Aluminium foil capacitor
B. Mica capacitor
C. Ceramic capacitor
D. Paper capacitor
112.

An uncharged conductor is placed near a charged conductor, then

A. the uncharged conductor gets charged by conduction
B. the uncharged conductor gets charged by induction and then attracted towards the charging body
C. the uncharged conductor is attracted first and then charged by induction
D. it remains as such
Answer» B. the uncharged conductor gets charged by induction and then attracted towards the charging body
113.

The presence of an uncharged conductor near a charged one increases the

A. charge of the charged conductor
B. capacity of the charged conductor
C. potential of the charged conductor
D. all of the above
Answer» B. capacity of the charged conductor
114.

Paper condenser is

A. always polarised
B. usually of fixed value
C. electrolytic condenser
D. a variable condenser
Answer» B. usually of fixed value
115.

Mica capacitors are characterised by all of thte following except

A. stable operation
B. accurate value
C. low leakage reactance
D. low losses
116.

A. 100 kV/m
B. 10 kV/m
C. 5 kV/m
D. 2 kV/m
117.

For a good 0.05 uF capacitor ohmmeter reading should

A. show low resistance momentarily and back off to a very high resis¬tance
B. show high resistance momentarily and then a very low resistance
C. go quickly to 50 ohm approximately and remain there
D. not move at all
Answer» A. show low resistance momentarily and back off to a very high resis¬tance
118.

A. infinity
B. few kilo ohms
C. few megaahms
D. zero
119.

Which of the following statements is correct ?

A. Mica capacitors are available in capacitance values of 5 to 20 \iF
B. Air capapitors have a black band to indicate the outside foil
C. Electrolytic capacitors must be connected in correct polarity
D. Ceramic capacitors must be con¬nected in correct polarity
Answer» C. Electrolytic capacitors must be connected in correct polarity
120.

Which of the following capacitors preferred for high frequency circuits ?

A. Air capacitor
B. Electrolytic capacitor
C. Mica capacitor
D. none of the above
121.

An electrolytic capacitor is generally made to provide

A. low capacitance
B. fixed capacitance
C. variable capacitance
D. large value of capacitance
Answer» D. large value of capacitance
122.

In order to remove static electricity from machinery

A. construct insulated cabins
B. insulate the machinery
C. ground the framework
D. humidify the surroundings
123.

If a third equal and similar charge is placed between two equal and similar charges, then this third charge will

A. move out of the field of influence of the two charges
B. remain in stable equilibrium
C. not be in equilibrium
D. be in unstable equilibrium
Answer» B. remain in stable equilibrium
124.

A region around a stationary electric charge has

A. an electric field
B. a magnetic field
C. both (a) and (b)
D. none of the above
125.

The minimum value of potential gradient in a cable occurs in

A. insulation
B. conductor
C. outer sheath
D. uniformly all over
126.

Dielectric strength of medium

A. increases with rise in temperature
B. increases with moisture content
C. is same for all insulating materials
D. none of the above
Answer» D. none of the above
127.

A. milli-coulomb
B. micro-coulomb
C. pico-coulomb
D. coulomb
128.

A. J/mm
B. C/m2
C. kV/mm
D. N/mm
129.

A positive and a negative charge are initially 50 mm apart. When they are moved close together so that they are now only 10 mm apart, the force between them will be

A. 5 times smaller than before
B. 5 times greater than before
C. 10 times greater than before
D. 25 times larger than before
Answer» D. 25 times larger than before
130.

A. Air
B. Glass
C. Bakelite
D. Paper
131.

When a dielectric is placed in an electric field the field strength

A. decreases
B. increases
C. reduces to zero
D. remain unchanged
132.

To prevent the generation of static charges on rubber or flat leather

A. surface is moistened
B. conductive dressing is done
C. oil compound dressing is done
D. talcum powder is sprayed on the surface
Answer» B. conductive dressing is done
133.

Which of the following capacitor is preferred in case of single phase motor ?

A. Mica capacitor
B. Paper capacitor
C. Electrolytic capacitor
D. Ceramic capacitor
134.

A capacitance is a circuit component that opposes the change in circuit

A. current
B. voltage
C. impedance
D. none of the above
135.

A condenser suitable for D.C. only is

A. metallic plate variable gang condenser
B. metallic paper capacitor
C. oil impregrated paper condenser
D. poled aluminium electrolytic condenser
Answer» D. poled aluminium electrolytic condenser
136.

In a capacitor, the electric charge is stored in

A. metal plates
B. dielectric
C. dielectric as well as metal plates
D. none of the above
Chapter: Magnetism and Electromagnetism
137.

Tesla is a unit of

A. field strength
B. inductance
C. flux density
D. flux
138.

A permeable substance is one

A. which is a good conductor
B. which is a bad conductor
C. which is a strong magnet
D. through which the magnetic lines of force can pass very easily
Answer» D. through which the magnetic lines of force can pass very easily
139.

The materials having low retentivity are suitable for making

A. weak magnets
B. temporary magnets
C. permanent magnets
D. none of the above
140.

A magnetic field exists around

A. iron
B. copper
C. aluminium
D. moving charges
141.

Ferrites are materials.

A. paramagnetic
B. diamagnetic
C. ferromagnetic
D. none of the above
142.

A. little
B. lower
C. higher
D. zero
143.

The direction of magnetic lines of force is

A. from south pole to north pole
B. from north pole to south pole
C. from one end of the magnet to another
D. none of the above
Answer» B. from north pole to south pole
144.

Which of the following is a vector quantity ?

A. Relative permeability
B. Magnetic field intensity
C. Flux density
D. Magnetic potential
145.

The two conductors of a transmission line carry equal current I in opposite directions. The force on each conductor is

A. proportional to 7
B. proportional to X
C. proportional to distance between the conductors
D. inversely proportional to I
146.

A material which is slightly repelled by a magnetic field is known as

A. ferromagnetic material
B. diamagnetic material
C. paramag>etic material
D. conducting material
147.

When an iron piece is placed in a magnetic field

A. the magnetic lines of force will bend away from their usual paths in order to go away from the piece
B. the magnetic lines of force will bend away from their usual paths in order to pass through the piece
C. the magnetic field will not be affected
D. the iron piece will break
Answer» B. the magnetic lines of force will bend away from their usual paths in order to pass through the piece
148.

Fleming's left hand rule is used to find

A. direction of magnetic field due to current carrying conductor
B. direction of flux in a solenoid
C. direction of force on a current car¬rying conductor in a magnetic field
D. polarity of a magnetic pole
Answer» C. direction of force on a current car¬rying conductor in a magnetic field
149.

The ratio of intensity of magnetisation to the magnetisation force is known as

A. flux density
B. susceptibility
C. relative permeability
D. none of the above
150.

Magnetising steel is normals difficult because

A. it corrodes easily
B. it has high permeability
C. it has high specific gravity
D. it has low permeability
Answer» D. it has low permeability
151.

The left hand rule correlates to

A. current, induced e.m.f. and direc¬tion of force on a conductor
B. magnetic field, electric field and direction of force on a conductor
C. self induction, mutual induction and direction of force on a conductor
D. current, magnetic field and direc¬tion of force on a conductor
Answer» D. current, magnetic field and direc¬tion of force on a conductor
152.

The unit of relative permeability is

A. henry/metre
B. henry
C. henry/sq. m
D. it is dimensionless
153.

A. zero
B. BLI
C. B2LI
D. BLI2
154.

The force between two long parallel conductors is inversely proportional to

B. current in one conductor
C. product of current in two conduc¬tors
D. distance between the conductors
Answer» D. distance between the conductors
155.

Materials subjected to rapid reversal of magnetism should have

A. large area oiB-H loop
B. high permeability and low hysteresis loss
C. high co-ercivity and high reten-tivity
D. high co-ercivity and low density
Answer» B. high permeability and low hysteresis loss
156.

Indicate which of the following material does not retain magnetism permanently.

A. Soft iron
B. Stainless steel
C. Hardened steel
D. None of the above
157.

A. cobalt
B. chromium
C. nickel
D. tungsten
158.

A. magnetoes
B. energy meters
C. transformers
D. loud-speakers
159.

Paramagnetic materials have relative permeability

A. slightly less than uuity
B. equal to unity
C. slightly more than unity
D. equal to that ferromagnetic mate rials
Answer» C. slightly more than unity
160.

A. ferromagnetic
B. paramagnetic
C. diamagnetic
D. bipolar
161.

A. 2 x 1(T2 N/m)
B. 2 x KT3 N/m
C. 2 x 10"5 N/m
D. 2x 1(T7 N/m)
162.

In the left hand rule, forefinger always represents

A. voltage
B. current
C. magnetic field
D. direction of force on the conductor
163.

A. Tungsten
B. Aluminium
C. Copper
D. Nickel
164.

Ferrites are a sub-group of

A. non-magnetic materials
B. ferro-magnetic materials
C. paramagnetic materials
D. ferri-magnetic materials
165.

Gilbert is a unit of

A. electromotive force
B. magnetomotive force
C. conductance
D. permittivity
166.

The working of a meter is based on the use of a permanent magnet. In order to protect the meter functioning from stray magnetic fields

A. meter is surrounded by strong magnetic fields
B. a soft iron shielding is used
C. a plastic shielding is provided
D. a shielding of anon-magnetic material is used
Answer» B. a soft iron shielding is used
167.

Reciprocal of permeability is

A. reluctivity
B. susceptibility
C. permittivity
D. conductance
168.

The relative permeability is less than unity is case of

A. ferromagnetic materials
B. ferrites
C. non-ferrous materials
D. diamagnetic materials
169.

Which of the following is the unit of magnetic flux density ?

A. weber
B. lumens
C. tesla
D. none of the above
170.

The magnetism left in the iron after exciting field has been removed is known as

A. permeance
B. residual magnetism
C. susceptance
D. reluctance
171.

Which of the following is not a unit of flux?

A. Maxwell
B. Telsa
C. Weber
D. All of the above
172.

A. Brass
B. Copper
C. Zinc
D. Ebonite
173.

A. 1 Wb/mm2
B. 1 Wb/m
C. 1 Wb/m2
D. 1 mWb/m2
174.

Out of the following statements, concerning an electric field, which statement is not true ?

A. The electric intensity is a vector quantity
B. The electric field intensity at a point is numerically equal to the force exerted upon a charge placed at that point
C. An electric field is defined as a point in space at which an electric charge would experienc* a force
D. Unit field intensity in the exertion of a force of one newton on a charge of one coulomb
Answer» B. The electric field intensity at a point is numerically equal to the force exerted upon a charge placed at that point
175.

When a magnet is in motion relative to a coil the induced e.m.f. does not depend upon

A. resistance of the coil
B. motion of the magnet
C. number of turns of the coil
D. pole strength of the magnet
Answer» A. resistance of the coil
176.

A. 10 webers
B. 10 webers
C. 10 webers
D. 10 webers
177.

When two ends of a circular uniform wire are joined to the terminals of a battery, the field at the centre of the circle

A. will be zero
B. will be infinite
C. will depend on the amount of e.m.f. applied
D. will depend on the radius of the circle
178.

Susceptibility is positive for

A. non-magnetic substances
B. diamagnetic substances
C. ferromagnetic substances
D. none of the above
179.

A. 100 N
B. 10 N
C. 1 N
D. 0.1 N
180.

A. 240 N
B. 24 N
C. 2.4 N
D. 0.24 N
181.

A. 2500 AT/m
B. 250 AT/m
C. 25 AT/m
D. 2.5 AT/m
182.

What is the magnitude and the direction of force per 1.1m length of a pair of conductors of a direct current linecarrying 10 amperes and spaced 100 mm apart ?

A. 22 x 10"8 N
B. 22 x 10"7 N
C. 22 x 10-6 N
D. 22 x 10"5 N
Answer» D. 22 x 10"5 N
183.

A. 63.38 N/Wb
B. 633.8 N/Wb
C. 6338 N/Wb
D. 63380 N/Wb
184.

A. reluctance
B. resistance
C. permeance
D. pole strength
185.

A. ampere-hour
B. watt
C. joule
D. coulomb
186.

The Biot-savart's law is a general modification of

A. Kirchhoffs law
B. Lenz's law
C. Ampere's law
187.

The most effective and quickest may of making a magnet from soft iron is by

A. placing it inside a coil carrying current
B. induction
C. the use of permanent magnet
D. rubbing with another magnet
Answer» A. placing it inside a coil carrying current
188.

A. copper
B. aluminium
C. soft iron
D. brass
189.

If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity

A. less than that of disc but in opposite direction
B. equal to that of disc and in the same direction
C. equal to that of disc and in the opposite direction
D. less than that of disc and in the same direction
Answer» D. less than that of disc and in the same direction
190.

A permanent magnet

A. attracts some substances and repels others
B. attracts all paramagnetic substan¬ces and repels others
C. attracts only ferromagnetic sub¬stances
D. attracts ferromagnetic substances and repels all others
Answer» A. attracts some substances and repels others
191.

The retentivity (a property) of material is useful for the construction of

A. permanent magnets
B. transformers
C. non-magnetic substances
D. electromagnets
192.

A. diamagnetic
B. paramagnetic
C. ferromagnetic
D. insulating
193.

A. ferromagnetic
B. paramagnetic
C. diamagnetic
D. dielectric
194.

Hysteresis loop in case of magnetically hard materials is more in shape as compared to magnetically soft materials.

A. circular
B. triangular
C. rectangular
D. none of the above
195.

A. M
B. M/2
C. 2 M
D. M/4
196.

A keeper is used to

A. change the direction of magnetic lines
B. amplify flux
C. restore lost flux
D. provide a closed path for flux
Answer» D. provide a closed path for flux
197.

Magnetic moment is a

A. pole strength
B. universal constant
C. scalar quantity
D. vector quantity
198.

The change of cross-sectional area of conductor in magnetic field will affect

A. reluctance of conductor
B. resistance of conductor
C. (a) and (b) b >th in the same way
D. none of the above
Answer» C. (a) and (b) b >th in the same way
199.

The uniform magnetic field is

A. the field of a set of parallel conductors
B. the field of a single conductor
C. the field in which all lines of mag¬netic flux are parallel and equidis¬tant
D. none of the above
Answer» C. the field in which all lines of mag¬netic flux are parallel and equidis¬tant
200.

The magneto-motive force is

A. the voltage across the two ends of exciting coil
B. the flow of an electric current
C. the sum of all currents embraced by one line of magnetic field
D. the passage of magnetic field through an exciting coil
Answer» C. the sum of all currents embraced by one line of magnetic field