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UNIT I - ELECTROMAGNETISM >> MCQs 1-50
1. The complete path followed by the magnetic
flux is called
a. electric circuit
b. magnetic circuit
c. electromagnetism
d. electric field
ans: b
2. Current carrying conductor is always surrounded by
a. magnetic field
b. electric field
c. Electricity
d. current
ans: a
3. The direction of magnetic field produced by current carrying conductor is given by
a. Lenz’s law
b. right hand thumb rule
c. Fleming’s left hand rule
d. Kirchoff’s law
ans: b
4. Imaginary lines of force originating from magnet is called
a. current
b. resistance
c. flux
d. magnetic field
ans: c
5. Region surrounded by magnet is called
a. magnetic field strength
b. magnetic field
c. electric field
d. resistance
ans: b
6. Lines of force is also called
a. flux
b. current
c. resistance
d. flux density
ans:a
7. Lines of force passing per unit area is called
a. magnetic field
b. magnetic flux
c. magnetic flux density
d. magnetic field strength
ans:c
8. unit of flux is
a. weber
b. wb/m2
c. Tesla
d. AT
ans:a
9. Unit of flux density is
a. wb/m2
b. wb
c. AT/wb
d. A
ans:a
10. Unit of magnetic field
a. wb/m2
b. wb
c. AT/wb
d. none of above
ans:b
11. Unit of reluctance is
a. AT/wb
b. AT
c. Tesla
d. Wb/A
ans:a
12. Opposition to the magnetic lines of force is called
a. Flux
b. resistance
c. susceptance
d. reluctance
ans:d
13. Unit of magnetic field strength is
a. AT/m
b. AT/wb
c.Tesla
d. ohms
ans: a
14. The force on two current carrying conductors in the same direction
a. have force of repulsion between them
b. have force of attraction between them
c. remains unaffected
d. none of above
ans: b
15. Magneto motive force is directly proportional to
a. no. of turns of coil
b. current through the coil
c. both a and b
d. none of above
ans: c
16. The term permeability for a material means
a. the no. of turns on an air core
b. the mmf required to produce one unit of magnetic flux
c. the ability of a material to conduct electricity through it
d. the ability of material to conduct magnetic lines of force
ans: d
17. An air gap is usually inserted in a magnetic circuit
a. to prevent saturation
b. increase flux
c. decrease flux
d. increase mmf
ans: a
18. A magnetic circuit requires 800 ampere turns to produce a certain amount of flux. If exciting coil of 100 turns has 5 ohms resistance, then the voltage to be applied to the exciting coil must be
a. 40V
b. 20 V
c.10V
d. 5V
ans: a
19. Permeability of a material is the ratio of
a. magnetic field to flux density
b. flux density to magnetic field strength
c. magnetic field strength to flux density
d. none of above
ans: b
20. The term saturation related to magnetic circuit means
a. magnetic field strength increases with current
b. flux density increases with current
c. flux density remains constant if magnetic field strength is increased
d. magnetic field strength remains constant if flux density is increased.
ans:c
21. The lines of force produced by coil completing their path through air, instead of intended path is called
a. useful flux
b. saturated flux
c. air flux
d. leakage flux
ans: d
22. The bulging of lines of force in air gap in a magnetic circuit is called
a. leaking flux
b. merging
c. fringing
d. scattering
ans: c
23. Relative permeability of vacuum is
a. 4Ï€ × 10-7 H/m
b. 1 H/m
c.1
d. 1⁄4 H/m
ans: c
24.MMF in magnetic circuit is analogous to
a. electric current in electric circuit
b. current density in conductor
c. electromotive force
d. resistance in electric circuit
ans:c
25. Reluctance is analogous to
a. emf in electric circuit
b. resistivity
c. conductivity
d. resistance in electric circuit
ans: d
26. The magnetic reluctance of a material
a. increases with increasing cross sectional area of material
b. does not vary with increasing the cross sectional area
c. decreases with increasing cross sectional area of material
d. decreases with increasing the length of material
ans: c
27. The correct relation stated as following is
a. ф = Nl/aμ0μr
b. NI = B× l/a μ0μr
c. N=H×l
d. NI = Ñ„ × l/μ0μr a
ans: d
28. The permeance in a magnetic circuit corresponds to
a. resistance in an electric circuit
b. emf in an electric circuit
c. conductivity in electric circuit
d. conductance in an electric circuit
ans: d
29. The ampere turns are
a. the product of the number of turns and current of the coil
b. the number of turns of a coil through which current is flowing
c. the currents of all turns of the coil
d. the turns of transformer winding
ans:a
30. What will be the current flowing through the ring shaped air core when number of turns is 800 and ampere turns are 3200
a. 0.25
b.2.5
c.4.0
d. 0.4
ans:c
31. Leakage factor is defined as the ratio of
a. flux in air gap by total flux
b. Total flux by useful flux
c. airgp flux by useful flux
d. total flux by flux produced by solenoid
ans: b
32. Effect of fringing in magnetic circuit is
a. it increases flux density
b. its effective area of air gap decreases
c. it decreases flux density
d. none of above
ans:c
33.The force experienced by unit north pole when placed at point in a magnetic field is called
a. magnetic field strength at that point
b. exerted force at that point
c.flux
d. magnetic field
ans:a
34. The mechanical force acting on current carrying on conductor when placed in magnetic field is given by relation
a. F= N dф/dt
b. F= Blv sinÓ¨
c. F= BIL sinÓ¨
d. F=L di/dt
ans: c
35. Which of the following has the highest magnetic permeability?
a. paramagnetic substances
b. diamagnetic substances
c. ferromagnetic substances
d. vacuum
ans: c
36. The perfect insulator for magnetic lines of force is
a. copper
b. rubber
c. glass
d. none of these
ans: d
37. The force between two parallel current carrying conductors is given by relation
a. I1I2 ×2× 10-7× l/d
b. I1 dl /I2 ×4Ï€× 10-7
c. I1I2 /2Ï€× 10-7
d. I12×4× 10-7ld
ans: a
39. The magnitude of force experienced by current carrying conductor placed in magnetic field depends on
a. value of flux
b. magnitude of current flowing through
conductor
c. direction of current
d. all of above
ans: d
40.Two current carrying conductor lying parallel and close to each other. They are carrying current in the opposite direction. The force between them is
a. repulsive
b. Attractive
c. Zero
d. none of these
ans: a
41. Two current carrying conductor lying parallel and close to each other. They are carrying current in the same direction. The force between them is
a. repulsive
b. Attractive
c. Zero
d. none of these
ans: b
42. Two current carrying conductor lying parallel and close to each other are exerting force of attraction on each other. The currents are
a. very high
b. in opposite direction
c. low
d. in the same direction
ans: d
43. Two current carrying conductor lying parallel and close to each other are exerting force of repulsion on each other. The currents are
a. very high2
b. in opposite direction
c. low
d. in the same direction
ans: b
44. Two conductors are carrying 1000A and 5000A currents respectively are 5cm apart. The force per meter length between two conductors is
a. 100 N/m
b. 40 N/m
c.30 N/m
d. 20 N/m
ans: d
45. Magnetic field strength due to N long straight current carrying conductors in the same direction is given by
a. H= NI/ 4Ï€d
b. H= I/ 2Ï€d
c. H= NI/ 2Ï€d
d. H=NI/l
ans: c
46. A conductor of 10cm length carrying current of 5A placed in uniform magnetic field of flux density 1.25T at 300 to the lines of flux. Force acting on conductor will be
a.0.3125N
b. 3.125N
c.1.325N
d. 5.321N
ans: a
47.Fleming’s left hand rule is used to find
a. Magnitude of induced emf in conductor
b. Direction of magnetic field in conductor
c. Direction of force on current carrying conductor
d. Magnitude of flux density
ans: c
48. Which statement is correct related to magnetic field produced due to current carrying conductor
a. direction of rotation of screw to advance in the direction of current gives the direction of magnetic field
b. If right hand curled fingers shows the
direction of current, thumb gives the direction of magnetic field
c. if direction of rotation of screw shows current ,tip gives the direction of magnetic field
d. all of these
ans: a
49. Force experienced by current carrying conductor when placed in magnetic field will be zero when
a. current in the conductor is maximum
b. Angle between conductor and field is zero
c. Both a &b
d. None of these
ans: b
50. Relative permeability is defined as the ratio of
a. magnetic field strength in a medium to flux
density in the same medium
b. Magnetic flux density in vacuum to magnetic
field strength in vacuum
c. Magnetic flux density in other medium to flux
density in vacuum
d. Magnetic flux density in vacuum to flux
density in other medium
ans: c
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