Magnetism and Electromagnetism Multiple choice Questions and Answers-2 (English)

1. An air gap is usually inserted in magnetic circuits to
(A) increase m.m.f.
(B) increase the flux
(C) prevent saturation
(D) none of the above
Ans: (C)

2. The relative permeability of a ferromagnetic material is
(A) less than one
(B) more than one
(C) more than 10
(D) more than 100 or 1000
Ans: (D)

3. The unit of magnetic flux is
(A) henry
(B) weber
(C) ampereturn/weber
(D) ampere/metre
Ans: (B)

4. Permeability in a magnetic circuit corresponds to______ in an electric circuit.
(A) resistance
(B) resistivity
(C) conductivity
(D) conductance
Ans: (C)

5. Reciprocal of permeability is
(A) reluctivity
(B) susceptibility
(C) permittivity
(D) conductance
Ans: A

6. The relative permeability is less than unity is case of
(A) ferromagnetic materials
(B) ferrites
(C) non-ferrous materials
(D) diamagnetic materials
Ans: D

7. Which of the following is the unit of magnetic flux density ?
(A) weber
(B) lumens
(C) tesla
(D) none of the above
Ans: C

8. The magnetism left in the iron after exciting field has been removed is known as
(A) permeance
(B) residual magnetism
(C) susceptance
(D) reluctance
Ans: B

9. Which of the following is not a unit of flux?
(A) Maxwell
(B) Telsa
(C) Weber
(D) All of the above
Ans: B

10. Which of the following is expected to have the maximum permeability ?
(A) Brass
(B) Copper
(C) Zinc
(D) Ebonite
Ans: D

11. Point out the wrong statement. Magnetic leakage is undesirable in electric machines because it
(A) lowers their power efficiency
(B) increases their cost of manufacture
(C) leads to their increased weight
(D) produces fringing
Ans: (A)

12. Relative permeability of vacuum is
(A) 1
(B) 1 H/m
(C) 1/4JI
(D) 4n x 10 H/m
Ans: (A)

13. Permanent magnets are normally made of
(A) alnico alloys
(B) aluminium
(C) cast iron
(D) wrought iron
Ans: (A)

14. Energy stored by a coil is doubled when its current is increased by percent.
(A) 25
(B) 50
(C)41.4
(D) 100
Ans: (C)

15. Those magnetic materials are best suited for making armature and transformer cores which have____permeability and_______hystersis loss.
(A) high, high
(B) low, high
(C) high, low
(D) low, low
Ans: (C)

16. The rate of rise of current through an inductive coil is maximum
(A) at 63.2% of its maximum steady value
(B) at the start of the current flow
(C) after one time constant
(D) near the final maximum value of current
Ans: (B)

17. A material which is slightly repelled by a magnetic field is known as
(A) ferromagnetic material
(B) diamagnetic material
(C) paramagnetic material
(D) conducting material
Ans: B

18. 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
Ans: B

19. 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 carrying conductor in a magnetic field
(D) polarity of a magnetic pole
Ans: C

20. A conductor of length L has current I passing through it, when it is placed parallel to a magnetic field. The force experienced by the conductor will be
(A) zero
(B) BLI
(C) B2LI
(D) BLI2
Ans: A