Magnetic Circuit Calculations — MCQs – EE

1. A magnetic circuit is analogous to an electric circuit in that it:
(A) Has magnetic flux instead of current
(B) Uses voltage instead of magnetomotive force
(C) Contains resistance instead of reluctance
(D) Has current instead of flux

2. The magnetomotive force (MMF) in a magnetic circuit is produced by:
(A) Current flowing through turns of a coil
(B) Voltage applied across the circuit
(C) Resistance of the core
(D) Capacitance of winding

3. The unit of magnetomotive force (MMF) is:
(A) Ampere-turn (AT)
(B) Weber
(C) Tesla
(D) Henry

4. The reluctance of a magnetic circuit is analogous to:
(A) Resistance in an electric circuit
(B) Capacitance in an electric circuit
(C) Inductance in an electric circuit
(D) Reactance in an AC circuit

5. The unit of magnetic flux is:
(A) Weber (Wb)
(B) Tesla (T)
(C) Ampere (A)
(D) Henry (H)

6. The flux density (B) is defined as:
(A) Flux per unit area
(B) Current per unit area
(C) Voltage per unit length
(D) MMF per unit volume

7. The unit of flux density (B) is:
(A) Tesla (T)
(B) Weber (Wb)
(C) Ampere-turn (AT)
(D) Henry per meter (H/m)

8. The permeability (μ) of a material represents:
(A) Its ability to conduct magnetic flux
(B) Its electrical conductivity
(C) Its resistance to current flow
(D) Its dielectric strength

9. The relative permeability (μr) is the ratio of:
(A) Permeability of material to permeability of free space
(B) Flux to current
(C) Voltage to flux
(D) Magnetizing current to flux

10. The magnetizing force (H) is defined as:
(A) MMF per unit length of magnetic path
(B) Flux per unit area
(C) Flux per unit reluctance
(D) Voltage per unit length

11. The unit of magnetic field strength (H) is:
(A) Ampere-turn per meter (AT/m)
(B) Weber per meter (Wb/m)
(C) Tesla per meter (T/m)
(D) Ampere (A)

12. The magnetization curve (B–H curve) of a material shows:
(A) Relation between flux density and magnetizing force
(B) Variation of current with voltage
(C) Variation of resistance with temperature
(D) Variation of power with frequency

13. The point beyond which the magnetic material saturates is known as:
(A) Saturation point
(B) Coercive point
(C) Remanence point
(D) Hysteresis point

14. The hysteresis loop shows:
(A) Relationship between B and H during magnetization and demagnetization
(B) Voltage–current relationship
(C) Load–speed characteristic
(D) Power–torque relationship

15. The area of the hysteresis loop represents:
(A) Energy loss per cycle per unit volume
(B) Magnetic flux density
(C) Permeability of material
(D) Magnetic energy stored

16. Soft magnetic materials are preferred for magnetic circuits because they:
(A) Have low hysteresis loss and high permeability
(B) Have high coercivity
(C) Have high resistivity
(D) Are mechanically stronger

17. Hard magnetic materials are used for:
(A) Permanent magnets
(B) Transformer cores
(C) Electromagnets
(D) Relays

18. In a series magnetic circuit, the total reluctance is equal to:
(A) Sum of individual reluctances
(B) Product of individual reluctances
(C) Reciprocal of sum of reciprocals
(D) Difference of reluctances

19. In a parallel magnetic circuit, the total reluctance is:
(A) Reciprocal of sum of reciprocals of individual reluctances
(B) Sum of individual reluctances
(C) Product of individual reluctances
(D) Difference of reluctances

20. Leakage flux in a magnetic circuit refers to:
(A) Flux that does not follow the intended magnetic path
(B) Main flux in the core
(C) Residual magnetism
(D) Hysteresis flux

21. The leakage coefficient is the ratio of:
(A) Total flux to useful flux
(B) Useful flux to leakage flux
(C) Magnetic flux to reluctance
(D) Flux density to field strength

22. The B–H curve of a non-magnetic material is:
(A) A straight line passing through the origin
(B) Highly nonlinear
(C) Closed loop
(D) Vertical

23. When the length of magnetic path is increased, the reluctance:
(A) Increases
(B) Decreases
(C) Remains constant
(D) Becomes zero

24. When the cross-sectional area of a magnetic path increases, the reluctance:
(A) Decreases
(B) Increases
(C) Remains same
(D) Becomes infinite

25. The permeability of air is approximately:
(A) 4π × 10⁻⁷ H/m
(B) 1 H/m
(C) 10⁻⁶ H/m
(D) 4π × 10⁻⁴ H/m

26. The flux density in the air gap of a magnetic circuit depends on:
(A) MMF and air-gap length
(B) Core loss
(C) Armature current
(D) Supply voltage

27. The energy stored in a magnetic field is proportional to:
(A) Square of flux density
(B) Flux only
(C) Reluctance
(D) Resistance

28. Residual magnetism in a magnetic material is represented on the B–H curve by:
(A) The point where H = 0 and B ≠ 0
(B) The point where B = 0
(C) The origin
(D) The saturation point

29. The coercive force is:
(A) The magnetizing force required to reduce flux density to zero
(B) The flux at saturation
(C) The residual flux
(D) The magnetizing current at start

30. The main purpose of magnetic circuit calculations is to:
(A) Determine the required number of turns and current to produce desired flux
(B) Calculate copper losses
(C) Design insulation
(D) Measure temperature rise