Electromagnetic Induction
Q. A changing magnetic field induces a current in a closed loop. What is this phenomenon called?
A.
Electromagnetic induction
B.
Magnetic resonance
C.
Electrolysis
D.
Magnetism
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Solution
This phenomenon is known as electromagnetic induction, where a changing magnetic field induces an electromotive force (EMF) in a conductor.
Correct Answer: A — Electromagnetic induction
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Q. A circular loop is placed in a uniform magnetic field. If the loop is rotated about its diameter, what happens to the induced EMF?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It becomes zero
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Solution
When the loop is rotated about its diameter, the angle between the magnetic field and the normal to the loop changes, but the magnetic flux remains constant. Therefore, the induced EMF becomes zero as there is no change in magnetic flux.
Correct Answer: D — It becomes zero
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Q. A coil of wire is placed in a changing magnetic field. What happens to the induced current if the resistance of the coil is increased?
A.
Induced current increases
B.
Induced current decreases
C.
Induced current remains the same
D.
Induced current becomes zero
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Solution
According to Ohm's law, if the resistance increases while the induced EMF remains constant, the induced current will decrease.
Correct Answer: B — Induced current decreases
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Q. A coil of wire is placed in a magnetic field. If the magnetic field strength is doubled, what happens to the induced EMF?
A.
It doubles
B.
It remains the same
C.
It halves
D.
It quadruples
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Solution
Doubling the magnetic field strength will double the induced EMF, as it is directly proportional to the magnetic field strength.
Correct Answer: A — It doubles
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Q. A coil of wire is placed in a magnetic field. If the magnetic field strength is increased, what happens to the induced EMF in the coil?
A.
It increases
B.
It decreases
C.
It remains the same
D.
It becomes zero
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Solution
According to Faraday's law of electromagnetic induction, the induced EMF in a coil is directly proportional to the rate of change of magnetic flux. Increasing the magnetic field strength increases the magnetic flux, thus increasing the induced EMF.
Correct Answer: A — It increases
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Q. A coil with 100 turns is placed in a magnetic field that changes at a rate of 0.5 T/s. What is the induced EMF in the coil?
A.
50 V
B.
100 V
C.
200 V
D.
25 V
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Solution
Using Faraday's law, EMF = -N * (dΦ/dt) = -100 * 0.5 = -50 V. The induced EMF is 50 V.
Correct Answer: B — 100 V
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Q. A coil with 100 turns is placed in a magnetic field that changes from 0.2 T to 0.5 T in 2 seconds. What is the induced EMF?
A.
15 V
B.
30 V
C.
5 V
D.
10 V
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Solution
Induced EMF (ε) = -N(dB/dt) = -100 * (0.5 - 0.2)/2 = -15 V.
Correct Answer: B — 30 V
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Q. A coil with 100 turns is placed in a magnetic field that changes from 0.5 T to 1.5 T in 2 seconds. What is the induced EMF?
A.
50 V
B.
100 V
C.
200 V
D.
400 V
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Solution
Induced EMF = -N * (ΔB/Δt) = -100 * ((1.5 - 0.5)/2) = -100 * (1/2) = -50 V. The magnitude is 50 V.
Correct Answer: B — 100 V
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Q. A loop of wire is moved into a magnetic field at a constant speed. What happens to the induced EMF as it enters the field?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It becomes zero
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Solution
As the loop enters the magnetic field, the rate of change of magnetic flux increases, leading to an increase in induced EMF.
Correct Answer: A — It increases
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Q. A loop of wire is moved into a magnetic field at a constant speed. What happens to the induced EMF as the loop enters the field?
A.
Induced EMF increases
B.
Induced EMF decreases
C.
Induced EMF remains constant
D.
Induced EMF becomes zero
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Solution
As the loop enters the magnetic field, the magnetic flux through the loop increases, leading to an increase in induced EMF.
Correct Answer: A — Induced EMF increases
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Q. A loop of wire is moved into a magnetic field at a constant speed. What is the effect on the induced current as the loop enters the field?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It becomes zero
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Solution
As the loop enters the magnetic field, the area of the loop within the field increases, leading to an increase in magnetic flux and thus an increase in the induced current according to Faraday's law.
Correct Answer: A — It increases
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Q. A loop of wire is moved into a uniform magnetic field at a constant speed. What happens to the induced EMF as it enters the field?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It becomes zero
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Solution
As the loop enters the magnetic field, the area exposed to the magnetic field increases, leading to an increase in the induced EMF.
Correct Answer: A — It increases
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Q. A loop of wire is placed in a uniform magnetic field. If the angle between the field and the normal to the loop is 60 degrees, what is the effective magnetic flux?
A.
0.5 B A
B.
0.866 B A
C.
0.866 B A²
D.
B A
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Solution
Effective magnetic flux (Φ) = B * A * cos(θ) = B * A * cos(60°) = 0.5 B A.
Correct Answer: B — 0.866 B A
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Q. A loop of wire is placed in a uniform magnetic field. If the field strength is increased, what happens to the induced EMF?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It becomes zero
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Solution
According to Faraday's law, an increase in magnetic field strength leads to an increase in the induced EMF.
Correct Answer: A — It increases
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Q. A magnetic field of 0.3 T is perpendicular to a circular loop of radius 0.1 m. What is the magnetic flux through the loop?
A.
0.03 Wb
B.
0.03 Tm²
C.
0.1 Wb
D.
0.1 Tm²
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Solution
Magnetic flux (Φ) = B * A = 0.3 T * π(0.1 m)² = 0.03 Wb.
Correct Answer: A — 0.03 Wb
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Q. A solenoid has a length of 1 m and a cross-sectional area of 0.01 m². If the magnetic field inside it is 0.4 T, what is the magnetic flux?
A.
0.004 Wb
B.
0.04 Wb
C.
0.4 Wb
D.
0.1 Wb
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Solution
Magnetic flux (Φ) = B * A = 0.4 T * 0.01 m² = 0.004 Wb.
Correct Answer: B — 0.04 Wb
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Q. A solenoid has a length of 1 m and a cross-sectional area of 0.01 m². If the magnetic field inside it is 0.2 T, what is the magnetic flux?
A.
0.002 Wb
B.
0.01 Wb
C.
0.02 Wb
D.
0.1 Wb
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Solution
Magnetic flux (Φ) = B * A. Here, Φ = 0.2 T * 0.01 m² = 0.002 Wb.
Correct Answer: C — 0.02 Wb
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Q. A transformer operates on the principle of electromagnetic induction. If the primary coil has 100 turns and the secondary coil has 50 turns, what is the relationship between the primary and secondary voltages?
A.
V_primary = 2 * V_secondary
B.
V_primary = 0.5 * V_secondary
C.
V_primary = V_secondary
D.
V_primary = 4 * V_secondary
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Solution
The voltage ratio in a transformer is given by the turns ratio. Therefore, V_primary/V_secondary = N_primary/N_secondary = 100/50 = 2, which means V_primary = 2 * V_secondary.
Correct Answer: A — V_primary = 2 * V_secondary
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Q. A transformer operates on the principle of electromagnetic induction. What is the primary function of a transformer?
A.
To increase voltage
B.
To decrease voltage
C.
To convert AC to DC
D.
To store energy
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Solution
A transformer is designed to increase or decrease the voltage in an AC circuit through electromagnetic induction, depending on the turns ratio of the primary and secondary coils.
Correct Answer: A — To increase voltage
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Q. A transformer operates on the principle of electromagnetic induction. What is the main purpose of a transformer?
A.
To increase or decrease voltage
B.
To store electrical energy
C.
To convert AC to DC
D.
To measure current
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Solution
A transformer is used to increase or decrease the voltage in an AC circuit based on the turns ratio of its coils.
Correct Answer: A — To increase or decrease voltage
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Q. A transformer works on the principle of:
A.
Electromagnetic induction
B.
Electrostatics
C.
Magnetic resonance
D.
Thermal conduction
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Solution
A transformer operates on the principle of electromagnetic induction, transferring energy between coils through a changing magnetic field.
Correct Answer: A — Electromagnetic induction
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Q. According to Faraday's law, the induced EMF in a circuit is directly proportional to what?
A.
The rate of change of magnetic flux
B.
The strength of the magnetic field
C.
The resistance of the circuit
D.
The length of the conductor
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Solution
Faraday's law states that the induced EMF is directly proportional to the rate of change of magnetic flux through the circuit.
Correct Answer: A — The rate of change of magnetic flux
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Q. According to Faraday's law, the induced EMF in a circuit is proportional to what?
A.
The rate of change of magnetic flux
B.
The strength of the magnetic field
C.
The resistance of the circuit
D.
The length of the conductor
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Solution
Faraday's law states that the induced EMF is directly proportional to the rate of change of magnetic flux through the circuit.
Correct Answer: A — The rate of change of magnetic flux
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Q. If a coil with a resistance of 10 ohms has an induced EMF of 20 volts, what is the induced current?
A.
2 A
B.
0.5 A
C.
10 A
D.
20 A
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Solution
Using Ohm's law (I = V/R), the induced current I = 20V / 10Ω = 2 A.
Correct Answer: A — 2 A
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Q. If a conductor is moved perpendicular to a magnetic field, what is the effect on the induced EMF?
A.
It is maximized
B.
It is minimized
C.
It becomes zero
D.
It fluctuates
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Solution
The induced EMF is maximized when the conductor moves perpendicular to the magnetic field lines.
Correct Answer: A — It is maximized
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Q. If a conductor moves through a magnetic field, what is the induced EMF dependent on?
A.
The speed of the conductor and the strength of the magnetic field
B.
The length of the conductor only
C.
The temperature of the conductor
D.
The type of material of the conductor
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Solution
The induced EMF is dependent on the speed of the conductor and the strength of the magnetic field it moves through.
Correct Answer: A — The speed of the conductor and the strength of the magnetic field
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Q. If a magnetic field is applied perpendicular to a loop of wire, what is the effect on the induced EMF?
A.
It is maximum
B.
It is minimum
C.
It is zero
D.
It fluctuates
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Solution
When a magnetic field is applied perpendicular to a loop of wire, the magnetic flux through the loop is maximized, resulting in maximum induced EMF according to Faraday's law.
Correct Answer: A — It is maximum
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Q. If a magnetic field of 0.1 T is perpendicular to a circular loop of radius 0.1 m, what is the magnetic flux through the loop?
A.
0.01 Wb
B.
0.03 Wb
C.
0.1 Wb
D.
0.05 Wb
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Solution
Magnetic flux (Φ) = B * A = B * πr². Here, A = π(0.1)² = 0.01π m². Thus, Φ = 0.1 * 0.01π = 0.01π Wb ≈ 0.0314 Wb.
Correct Answer: A — 0.01 Wb
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Q. If the area of a loop in a magnetic field is doubled while keeping the magnetic field strength constant, what happens to the magnetic flux?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
Magnetic flux (Φ) is given by Φ = B * A. If the area (A) is doubled, the magnetic flux also doubles.
Correct Answer: A — It doubles
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Q. If the area of a loop is doubled while the magnetic field remains constant, how does the induced EMF change?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Quadruples
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Solution
Induced EMF is proportional to the area of the loop. If the area is doubled, the induced EMF also doubles.
Correct Answer: A — Doubles
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