Self and mutual inductance and eddy currents - Question Bank

1. The self-inductance of a straight wire is:
A) Zero.
B) Very large.
C) Comparable to a solenoid.
D) Dependent on the current.
2. Eddy currents are used in:
A) Electric generators.
B) Transformers.
C) Induction motors.
D) Induction furnaces.
3. Which of the following is a unit of inductance?
A) Volt-second/Ampere
B) Ampere-second/Volt
C) Volt/Ampere-second
D) Ampere/Volt-second
4. If two coils with self-inductances L1 and L2 are connected in series such that their fluxes add, the total inductance is:
A) L1 + L2
B) L1 + L2 + 2M
C) L1 + L2 - 2M
D) sqrt(L1*L2)
5. The self-inductance of a coil is independent of:
A) The number of turns.
B) The area of the cross-section.
C) The length of the coil.
D) The current flowing through it.
6. Eddy currents are induced when a conductor moves relative to a magnetic field or when:
A) The conductor is heated.
B) The magnetic field through the conductor changes.
C) The conductor is placed in a vacuum.
D) The conductor is insulated.
7. If the rate of change of current in a coil of inductance 0.5 H is 20 A/s, the magnitude of the induced emf is:
A) 5 V
B) 10 V
C) 20 V
D) 40 V
8. The coefficient of coupling 'k' between two coils is zero when:
A) The coils are tightly wound and close together.
B) There is no magnetic flux linkage between the coils.
C) The coils are identical.
D) The coils are connected in series.
9. Which of the following statements about inductance is correct?
A) Inductance is the ratio of voltage to current.
B) Inductance is the ratio of magnetic flux to current.
C) Inductance is the ratio of induced emf to the rate of change of current.
D) Inductance is the ratio of magnetic field to current.
10. A solid iron core is used in a transformer to:
A) Increase resistance.
B) Reduce eddy currents.
C) Increase magnetic flux linkage.
D) Decrease magnetic flux linkage.
11. Mutual inductance is a measure of:
A) How much emf is induced in a coil due to its own changing current.
B) How much emf is induced in one coil due to a changing current in another coil.
C) The ability of a coil to store magnetic energy.
D) The resistance to the flow of AC current.
12. The unit of magnetic flux is:
A) Tesla
B) Ampere-meter
C) Weber
D) Henry
13. If the current in a coil of self-inductance L is I, the magnetic energy stored is proportional to:
A) I
B) I^2
C) sqrt(I)
D) 1/I
14. Eddy current losses in transformers are reduced by:
A) Increasing the core's permeability.
B) Using a thicker core.
C) Using thin, insulated laminations for the core.
D) Increasing the frequency of the AC supply.
15. The direction of the induced current in Lenz's law is such that it:
A) Strengthens the magnetic field.
B) Weakens the magnetic field.
C) Opposes the change in magnetic flux.
D) Is in the same direction as the change in magnetic flux.
16. A coil of inductance 2 H is connected to a DC source. If the current is switched off instantaneously, the induced emf will be:
A) Zero.
B) Finite and depends on the rate of current change.
C) Infinite.
D) Equal to the applied voltage.
17. For two inductively coupled coils, the coupling coefficient 'k' is defined as:
A) k = M / sqrt(L1 * L2)
B) k = sqrt(L1 * L2) / M
C) k = M * sqrt(L1 * L2)
D) k = M / (L1 + L2)
18. Which of the following applications utilizes the principle of eddy currents?
A) Electric motor.
B) Generator.
C) Induction heating.
D) Loudspeaker.
19. The coefficient of mutual induction between two coils is 10 mH. If a current of 2 A flows through one coil, the magnetic flux linked with the other coil is:
A) 20 mWb
B) 10 mWb
C) 5 mWb
D) 2 mWb
20. If the number of turns in a coil is doubled, its self-inductance will:
A) Halve.
B) Double.
C) Become four times.
D) Remain the same.
21. The unit of magnetic flux density is:
A) Weber
B) Henry
C) Tesla
D) Ampere
22. Eddy currents are induced in a metallic core when it is placed in a:
A) Constant magnetic field.
B) Changing magnetic field.
C) Uniform electric field.
D) Non-uniform electric field.
23. The energy stored in an inductor is given by:
A) LI^2
B) 1/2 * LI^2
C) LI
D) 1/2 * L^2 * I
24. In a variable inductor, the inductance is changed by:
A) Changing the resistance.
B) Changing the voltage.
C) Changing the geometry or position of the core.
D) Changing the frequency of the current.
25. Which of the following factors does NOT affect the mutual inductance between two coils?
A) The number of turns in each coil.
B) The relative permeability of the medium.
C) The current flowing in one of the coils.
D) The distance between the coils.
26. The property of a coil that opposes the change in current flowing through it is called:
A) Conductance
B) Resistance
C) Capacitance
D) Inductance
27. If the magnetic flux through a coil is doubled, the induced emf will:
A) Double.
B) Halve.
C) Remain the same.
D) Become zero.
28. The self-inductance of a circular coil of radius 'r' and 'N' turns carrying current 'I' is approximately proportional to:
A) r
B) r^2
C) 1/r
D) 1/r^2
29. Eddy currents are also known as:
A) Displacement currents.
B) Circulating currents.
C) Surface currents.
D) Induced currents.
30. The magnetic flux linkage in a coil is given by NΦ. If the current changes by ΔI and the flux changes by ΔΦ, the induced emf is given by:
A) -Δ(NΦ)/Δt
B) -NΔΦ/Δt
C) -ΔI/Δt
D) -NΔI/Δt
31. A changing magnetic flux through a conductor induces:
A) A steady current.
B) An emf.
C) A static charge.
D) A magnetic pole.
32. The ratio of self-inductance to mutual inductance for two tightly coupled coils is:
A) Always equal to 1.
B) Always greater than 1.
C) Always less than 1.
D) Can be greater than, less than, or equal to 1 depending on the coils.
33. In a transformer, eddy currents are minimized by:
A) Using a thick core.
B) Using a solid core.
C) Laminating the core with insulating layers.
D) Increasing the number of turns.
34. The self-inductance of a coil depends on its:
A) Resistance.
B) Current.
C) Geometry and magnetic properties of the core.
D) Applied voltage.
35. Two coils have a mutual inductance of 5 mH. If the current in the first coil changes from 1 A to 2 A in 0.05 s, the magnitude of the induced emf in the second coil is:
A) 0.1 V
B) 0.5 V
C) 1 V
D) 0.05 V
36. If the current in a coil changes from 0 to 2 A in 0.1 s and the induced emf is 10 V, the self-inductance of the coil is:
A) 1 H
B) 0.5 H
C) 2 H
D) 0.1 H
37. The coefficient of self-inductance of a coil is numerically equal to the:
A) Magnetic flux linkage when a unit current flows through the coil.
B) Induced emf when a unit current flows through the coil.
C) Induced emf when the current changes at a unit rate.
D) Magnetic field produced by a unit current.
38. Eddy currents are undesirable in:
A) Induction furnaces.
B) Magnetic braking systems.
C) Transformers.
D) Speedometers.
39. Which of the following is a method to reduce eddy currents?
A) Using a solid core.
B) Increasing the resistance of the core.
C) Using a laminated core.
D) Increasing the magnetic field strength.
40. Mutual inductance (M) between two coils is defined by the relation:
A) M = N_1 * Phi_21 / I_1
B) M = N_2 * Phi_12 / I_2
C) M = N_1 * Phi_12 / I_1 = N_2 * Phi_21 / I_2
D) M = I_1 * I_2 / Phi_12
41. The self-inductance of a long solenoid is directly proportional to:
A) The square of its length.
B) The square of the number of turns per unit length.
C) The inverse of its cross-sectional area.
D) The inverse of the number of turns.
42. Lenz's Law is a consequence of the conservation of:
A) Charge
B) Energy
C) Momentum
D) Mass
43. The phenomenon of electromagnetic induction is described by:
A) Ohm's Law
B) Ampere's Law
C) Faraday's Law
D) Coulomb's Law
44. Eddy currents are:
A) Currents flowing in a straight wire.
B) Currents induced in a conductor when it is exposed to a changing magnetic field.
C) Currents that flow only in AC circuits.
D) Currents that flow in the direction of the applied voltage.
45. Which physical quantity is represented by the symbol 'L' in electrical circuits?
A) Resistance
B) Capacitance
C) Inductance
D) Conductance
46. What is the SI unit of magnetic flux?
A) Tesla
B) Weber
C) Henry
D) Gauss
47. Mutual inductance between two coils depends on:
A) Their relative orientation and geometry.
B) The magnetic permeability of the medium between them.
C) The distance between the coils.
D) All of the above.
48. The unit of inductance is:
A) Farad
B) Henry
C) Weber
D) Tesla
49. What is self-inductance?
A) The ability of a coil to oppose changes in its own magnetic flux.
B) The ability of a coil to induce current in a nearby coil.
C) The measure of induced voltage in a circuit.
D) The resistance to the flow of alternating current.
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