Faraday’s law, Lenz’s law and induced emf - Question Bank

1. A magnetic flux of 0.1 Wb passes through a coil of 200 turns. If the flux is reduced to zero in 0.01 seconds, the average induced emf is:
A) 2 V
B) 20 V
C) 200 V
D) 2000 V
2. According to Lenz's Law, the induced current creates a magnetic field that:
A) Strengthens the original magnetic field.
B) Weakens the original magnetic field.
C) Opposes the change in magnetic flux.
D) Is perpendicular to the original magnetic field.
3. If the number of turns in a coil is increased, what happens to the induced emf for the same rate of change of flux?
A) Decreases
B) Increases
C) Remains the same
D) Becomes zero
4. Which of the following is NOT a method to induce emf in a coil?
A) Changing the magnetic field strength.
B) Rotating the coil in a uniform magnetic field.
C) Increasing the resistance of the coil.
D) Changing the area of the coil in a magnetic field.
5. The induced emf is proportional to the rate of change of magnetic flux. This statement is the essence of:
A) Lenz's Law
B) Faraday's Law
C) Ampere's Law
D) Gauss's Law
6. When a coil is rotated in a uniform magnetic field, the induced emf varies sinusoidally with:
A) Time
B) Angle
C) Magnetic field strength
D) Number of turns
7. A metal rod of length 1 m is moving perpendicular to a magnetic field of 0.5 T with a velocity of 10 m/s. The induced emf across the ends of the rod is:
A) 0.5 V
B) 5 V
C) 10 V
D) 50 V
8. If the rate of change of magnetic flux is uniform, the induced emf is:
A) Zero
B) Variable
C) Constant
D) Infinite
9. The phenomenon of electromagnetic induction was discovered by:
A) Hans Christian Ørsted
B) André-Marie Ampère
C) Michael Faraday
D) James Clerk Maxwell
10. A conductor of length L moves with velocity v perpendicular to a magnetic field B. The induced emf is:
A) BLv
B) B/Lv
C) Lv/B
D) 0
11. If the magnetic field through a coil is reversed, the induced emf will:
A) Remain the same.
B) Reverse its direction.
C) Become zero.
D) Become infinite.
12. Which quantity is conserved if Lenz's law is violated?
A) Charge
B) Mass
C) Energy
D) Momentum
13. Lenz's law is most useful for determining:
A) The magnitude of induced emf.
B) The number of turns in the coil.
C) The direction of induced current.
D) The resistance of the circuit.
14. The magnetic flux through a closed loop is given by Φ(t) = 3t² + 2t + 1 Weber. The induced emf at t = 2 seconds is:
A) 14 V
B) 16 V
C) 26 V
D) 30 V
15. When a conductor moves in a non-uniform magnetic field, an emf is induced. This is an example of:
A) Static Induction
B) Dynamic Induction
C) Faraday's Law
D) Lenz's Law
16. Which of the following is a condition for electromagnetic induction?
A) A stationary magnet and a stationary coil.
B) A moving charge in a stationary magnetic field.
C) A relative motion between a conductor and a magnetic field.
D) A stationary conductor in a stationary magnetic field.
17. If the area of a rectangular loop in a uniform magnetic field is halved, the magnetic flux through the loop will:
A) Double
B) Remain unchanged
C) Halve
D) Become zero
18. The unit of magnetic flux linkage is:
A) Weber
B) Tesla
C) Ampere
D) Volt-second
19. According to Lenz's law, the induced current opposes the change in magnetic flux. This opposition requires:
A) Energy input
B) No energy
C) Charge separation
D) A constant magnetic field
20. A coil has 50 turns and the flux through it changes from 0.2 Wb to 0.6 Wb in 0.05 seconds. The magnitude of the induced emf is:
A) 100 V
B) 200 V
C) 400 V
D) 500 V
21. If a loop of wire is moved such that it cuts magnetic field lines, an emf is induced across the ends of the loop. This is known as:
A) Mutual Induction
B) Self Induction
C) Motional EMF
D) Induced EMF
22. Which of the following statements about magnetic flux is correct?
A) Magnetic flux is a scalar quantity.
B) Magnetic flux is a vector quantity.
C) Magnetic flux is always zero in a closed surface.
D) Magnetic flux is always positive.
23. A coil is connected to a battery. If the resistance of the coil is suddenly increased, the induced emf in the coil will be:
A) Zero
B) Positive
C) Negative
D) Variable
24. The direction of induced current in a closed circuit is such that it opposes the very cause which produces it. This is the statement of:
A) Faraday's Law
B) Ampere's Law
C) Lenz's Law
D) Biot-Savart Law
25. When a magnet is pushed into a coil connected to a galvanometer, the galvanometer needle deflects. If the magnet is pulled out, the needle will:
A) Deflect in the same direction.
B) Deflect in the opposite direction.
C) Not deflect.
D) Deflect twice.
26. The self-inductance of a coil is defined as the ratio of:
A) Magnetic flux to the current.
B) Induced emf to the rate of change of current.
C) Magnetic flux linkage to the current.
D) Current to the magnetic flux.
27. A current-carrying wire is moved perpendicular to a magnetic field. Will there be an induced emf in the wire?
A) Yes, if the magnetic field is changing.
B) Yes, if the wire is moving.
C) No, only a changing magnetic flux induces emf.
D) Yes, due to the magnetic force on the moving charges.
28. If the rate of change of magnetic flux through a coil of N turns is doubled, the induced emf will be:
A) Halved
B) Doubled
C) Unchanged
D) Tripled
29. Which of the following is a direct consequence of Faraday's Law of Induction?
A) The operation of electric motors.
B) The generation of electricity in power plants.
C) The magnetic effect of electric current.
D) The force on a charged particle in a magnetic field.
30. A circular coil is placed in a uniform magnetic field. If the coil is rotated about an axis lying in its plane, the induced emf will be:
A) Zero
B) Maximum when the plane of the coil is perpendicular to the field.
C) Maximum when the plane of the coil is parallel to the field.
D) Constant.
31. In the equation E = -N (dΦ/dt), if the magnetic flux is changing at a constant rate, the induced emf will be:
A) Variable
B) Zero
C) Constant
D) Infinite
32. What is the formula for magnetic flux (Φ) through a surface area A in a uniform magnetic field B?
A) Φ = B / A
B) Φ = A / B
C) Φ = B ⋅ A
D) Φ = B + A
33. A change in magnetic flux is essential for electromagnetic induction. This change can be achieved by:
A) Changing the magnetic field strength.
B) Changing the area of the loop.
C) Changing the orientation of the loop with respect to the field.
D) All of the above.
34. The unit of magnetic flux density (magnetic field strength) is:
A) Weber
B) Tesla
C) Farad
D) Henry
35. If a conducting loop is suddenly moved into a region of uniform magnetic field, Lenz's law states that the induced current will flow in a direction that:
A) Opposes the motion.
B) Assists the motion.
C) Opposes the magnetic field.
D) Assists the magnetic field.
36. A square loop of side 'a' is placed in a magnetic field B. If the loop is pulled out of the field at a constant speed v, what is the rate of change of flux?
A) Bav
B) Ba
C) Bv
D) 0
37. The induced emf can be generated by:
A) A stationary charge.
B) A changing magnetic field.
C) A constant electric field.
D) A stationary current.
38. Consider a solenoid. If the current through the solenoid is increased, the magnetic flux through a coil placed inside the solenoid will:
A) Decrease
B) Remain constant
C) Increase
D) Become zero
39. A bar magnet is dropped through a copper ring. What will happen to the magnet as it falls?
A) It will fall with constant acceleration g.
B) It will accelerate faster than g.
C) It will fall with an acceleration less than g.
D) It will stop inside the ring.
40. The induced emf in a circuit is given by E = -N (dΦ/dt). What does the negative sign signify?
A) The induced emf is always negative.
B) The induced emf is opposite in direction to the change in flux.
C) The induced emf is equal to the change in flux.
D) The number of turns is negative.
41. If the magnetic flux through a loop decreases, the induced current will flow in a direction that creates a magnetic field:
A) Opposing the original field.
B) In the same direction as the original field.
C) Perpendicular to the original field.
D) That is zero.
42. Which of the following scenarios will NOT induce an emf in a coil?
A) Moving a magnet towards the coil.
B) Changing the current in a nearby coil.
C) Rotating the coil in a uniform magnetic field.
D) Keeping the coil stationary in a constant magnetic field.
43. The unit of magnetic flux is:
A) Tesla
B) Weber
C) Ampere-meter
D) Henry
44. When a magnetic pole is moved towards a metallic ring, the induced current in the ring will:
A) Create a pole similar to the approaching pole.
B) Create a pole opposite to the approaching pole.
C) Not induce any current if the ring is a perfect insulator.
D) Always flow in the same direction regardless of the approaching pole.
45. A coil with 100 turns has a magnetic flux of 0.05 Wb passing through it. If this flux is reduced to 0.01 Wb in 0.1 seconds, what is the average induced emf?
A) 10 V
B) 20 V
C) 40 V
D) 50 V
46. If the magnetic flux through a coil is changing at a rate of 5 Wb/s, what is the magnitude of the induced emf?
A) 0.5 V
B) 5 V
C) 50 V
D) 0 V
47. Lenz's law helps determine which aspect of the induced current?
A) Magnitude
B) Frequency
C) Direction
D) Phase
48. Lenz's law is a consequence of the law of conservation of:
A) Charge
B) Momentum
C) Energy
D) Mass
49. According to Faraday's second law of electromagnetic induction, the magnitude of the induced emf in a circuit is directly proportional to:
A) The magnetic field strength.
B) The area of the loop.
C) The rate of change of magnetic flux through the circuit.
D) The resistance of the circuit.
50. Faraday's first law of electromagnetic induction states that:
A) An induced emf is proportional to the rate of change of magnetic flux.
B) A changing magnetic flux induces an electromotive force (emf).
C) The direction of the induced current opposes the change in magnetic flux.
D) The induced emf is equal to the rate of change of magnetic flux.
All Question Banks
E-Book Faraday’s law, Lenz’s law and induced emf One Line Questions Faraday’s law, Lenz’s law and induced emf Online Test Faraday’s law, Lenz’s law and induced emf