21. Reluctance is ________________ to the area of cross-section the material.
A. Directly proportional
B. Inversely proportional
C. Not related
D. Equal
Answer: B
The formula for reluctance is:
S = l/(µ0 µr×A..
From the formula, we can see that reluctance is inversely proportional to the area of a cross-section of the material.
22. When the length of the material increases, what happens to reluctance?
A. Increases
B. Decreases
C. Remains the same
D. Becomes zero
Answer: A
Reluctance is directly proportional to the length of the material hence as length increases, reluctance also increases.
23. When the area of a cross-section of the material increases, what happens to reluctance?
A. Increases
B. Decreases
C. Remains the same
D. Becomes zero
Answer: B
Reluctance is inversely proportional to the area of a cross-section of the material hence as area increases, reluctance decreases.
24. Unit of reluctance is?
A. AWb
B. A2/Wb
C. Wb/A
D. A/Wb
Answer: D
Reluctance is magnetomotive force per unit flux,
So the unit of reluctance = unit of MMF / unit of magnetic flux = A/Wb.
25. The electrical equivalent of reluctance is?
A. Resistance
B. Inductance
C. Capacitance
D. Conductance
Answer: A
Resistance is the opposition to the flow of charge, similarly, reluctance is the opposition to the flow of magnetic flux.
26. As the magnetic field strength increases, reluctance?
A. Increases
B. Decreases
C. Remains the same
D. Becomes zero
Answer: A
Reluctance is directly proportional to the strength of the magnetic field, hence as the strength of the magnetic field increases, the reluctance increases.
27. As the magnetic flux density increases, the reluctance _____________
A. Increases
B. Decreases
C. Remains the same
D. Becomes zero
Answer: B
Reluctance is inversely proportional to the magnetic flux density, hence as magnetic flux density increases, reluctance decreases.
28. Calculate the reluctance when the magnetomotive force is 10A turns and the flux is 5Wb.
A. 0.5A/Wb
B. 5A/Wb
C. 10A/Wb
D. 2A/Wb
Answer: D
We know that:
F = ϕ×S
Substituting the given values from the question:
S = 2A/Wb.
29. Ohm’s law for magnetic circuits is _________
A. F = ϕS
B. F = ϕ/S
C. F = ϕ2S
D. F = ϕ/S2
Answer: A
Ohm’s law for magnetic circuits states that the MMF is directly proportional to the magnetic flux where reluctance is the constant of proportionality.
30. What happens to the MMF when the magnetic flux decreases?
A. Increases
B. Decreases
C. Remains constant
D. Becomes zero
Answer: B
Ohm’s law for the magnetic circuits states that the MMF is directly proportional to the magnetic flux hence as the magnetic flux decreases, the MMF also decreases.
