Magnetism & EMI
Q. If the magnetic field around a closed loop is constant, what can be said about the current through the loop?
A.
It is zero
B.
It is variable
C.
It is constant
D.
It is infinite
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Solution
If the magnetic field around a closed loop is constant, the current through the loop must also be constant according to Ampere's Law.
Correct Answer: C — It is constant
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Q. If the magnetic field in a region is uniform, what is the shape of the magnetic field lines?
A.
Straight lines
B.
Curved lines
C.
Concentric circles
D.
Random
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Solution
In a uniform magnetic field, the magnetic field lines are straight and parallel.
Correct Answer: A — Straight lines
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Q. If the magnetic field strength is doubled, what happens to the force on a charged particle moving perpendicular to the field?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
The force on a charged particle is directly proportional to the magnetic field strength, so if the magnetic field strength is doubled, the force also doubles.
Correct Answer: A — It doubles
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Q. If the magnetic field strength is doubled, what happens to the induced EMF in a coil with a constant number of turns and area?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
According to Faraday's law, the induced EMF is directly proportional to the rate of change of magnetic flux, which depends on the magnetic field strength.
Correct Answer: A — It doubles
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Q. If the magnetic field strength is doubled, what happens to the magnetic force on a charged particle moving perpendicular to the field?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Quadruples
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Solution
The magnetic force on a charged particle is given by F = qvB sin(θ). If the magnetic field strength B is doubled, the force F also doubles, assuming charge q and velocity v remain constant.
Correct Answer: A — Doubles
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Q. If the magnetic field through a loop is doubled while the area remains constant, what happens to the magnetic flux?
A.
Magnetic flux doubles
B.
Magnetic flux halves
C.
Magnetic flux remains the same
D.
Magnetic flux becomes zero
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Solution
Magnetic flux is given by the product of magnetic field strength and area. If the magnetic field is doubled, the magnetic flux also doubles.
Correct Answer: A — Magnetic flux doubles
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Q. If the magnetic field through a loop is increased uniformly, what happens to the induced current in the loop?
A.
It flows in the direction of the magnetic field
B.
It flows in the opposite direction to the magnetic field
C.
It remains constant
D.
It stops flowing
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Solution
According to Lenz's law, the induced current will flow in the opposite direction to oppose the increase in magnetic flux.
Correct Answer: B — It flows in the opposite direction to the magnetic field
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Q. If the magnetic field through a loop is increasing at a constant rate, what can be said about the induced current?
A.
It is constant
B.
It is increasing
C.
It is decreasing
D.
It is zero
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Solution
If the magnetic field is increasing at a constant rate, the induced EMF is also increasing, which means the induced current is increasing.
Correct Answer: B — It is increasing
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Q. If the peak current in an AC circuit is 5 A, what is the average current over one complete cycle?
A.
5 A
B.
2.5 A
C.
0 A
D.
7.07 A
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Solution
The average current over one complete cycle is I_avg = I_peak/√2 = 5/√2 = 2.5 A.
Correct Answer: B — 2.5 A
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Q. If the peak voltage of an AC source is 200 V, what is the RMS voltage?
A.
100 V
B.
141.42 V
C.
200 V
D.
282.84 V
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Solution
The RMS voltage (V_rms) is given by V_rms = V_peak / √2. Therefore, V_rms = 200 V / √2 = 141.42 V.
Correct Answer: B — 141.42 V
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Q. If the peak voltage of an AC source is 220 V, what is the RMS voltage?
A.
110 V
B.
154 V
C.
220 V
D.
311 V
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Solution
The RMS voltage (V_rms) is given by V_rms = V_peak / √2. Therefore, V_rms = 220 V / √2 = 110 V.
Correct Answer: A — 110 V
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Q. If the radius of a circular loop carrying current is doubled, how does the magnetic field at the center change?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
The magnetic field at the center of a circular loop is inversely proportional to the radius; thus, doubling the radius halves the magnetic field.
Correct Answer: B — It halves
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Q. If the radius of a circular loop carrying current is doubled, what happens to the magnetic field at the center of the loop?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
The magnetic field at the center of a circular loop is given by B = (μ₀I)/(2r). If the radius is doubled, the magnetic field strength is halved.
Correct Answer: B — It halves
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Q. If the radius of a circular loop carrying current is halved, how does the magnetic field at the center change?
A.
Remains the same
B.
Doubles
C.
Halves
D.
Quadruples
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Solution
The magnetic field at the center is inversely proportional to the radius, so it quadruples.
Correct Answer: D — Quadruples
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Q. If the rate of change of current in an inductor is 2 A/s, what is the induced EMF if the inductance is 3 H?
A.
6 V
B.
3 V
C.
2 V
D.
1 V
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Solution
Induced EMF (ε) = -L(dI/dt) = -3 H * 2 A/s = -6 V.
Correct Answer: A — 6 V
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Q. If the resistance in a circuit is doubled while the voltage remains constant, what happens to the current?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Increases exponentially
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Solution
According to Ohm's law (V = IR), if resistance (R) is doubled and voltage (V) remains constant, the current (I) will be halved.
Correct Answer: B — Halves
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Q. If the resistance of a circuit is 10 ohms and the induced EMF is 20 V, what is the induced current?
A.
2 A
B.
0.5 A
C.
10 A
D.
5 A
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Solution
Using Ohm's law, I = V/R. Here, I = 20 V / 10 Ω = 2 A.
Correct Answer: A — 2 A
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Q. If the resistance of a circuit is doubled while keeping the induced EMF constant, what happens to the induced current?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It becomes zero
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Solution
According to Ohm's law (I = V/R), if the resistance is doubled while the voltage (induced EMF) remains constant, the current will be halved.
Correct Answer: B — It halves
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Q. If two parallel wires carry currents in the same direction, what is the interaction between the magnetic fields they produce?
A.
They repel each other
B.
They attract each other
C.
No interaction
D.
They cancel each other out
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Solution
Two parallel wires carrying currents in the same direction will attract each other due to the magnetic fields they produce.
Correct Answer: B — They attract each other
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Q. If two parallel wires carry currents in the same direction, what is the nature of the force between them?
A.
Attractive
B.
Repulsive
C.
No force
D.
Depends on the distance
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Solution
Two parallel wires carrying currents in the same direction experience an attractive force between them.
Correct Answer: A — Attractive
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Q. In a circular loop of radius R carrying a current I, what is the magnetic field at the center of the loop according to the Biot-Savart Law?
A.
B = (μ₀I)/(2R)
B.
B = (μ₀I)/(4R)
C.
B = (μ₀I)/(R)
D.
B = (μ₀I)/(πR)
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Solution
The magnetic field at the center of a circular loop of radius R carrying current I is given by B = (μ₀I)/(2R).
Correct Answer: A — B = (μ₀I)/(2R)
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Q. In a circular loop of radius R carrying a current I, what is the magnetic field at the center of the loop?
A.
μ₀I/(2R)
B.
μ₀I/(4R)
C.
μ₀I/(2πR)
D.
μ₀I/(4πR)
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Solution
The magnetic field B at the center of a circular loop of radius R carrying current I is given by B = μ₀I/(2R).
Correct Answer: A — μ₀I/(2R)
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Q. In a circular path of radius r around a long straight wire carrying current I, what is the line integral of the magnetic field?
A.
0
B.
μ₀I
C.
μ₀I/2
D.
μ₀I/4
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Solution
The line integral of B around the path is equal to μ₀I by Ampere's Law.
Correct Answer: B — μ₀I
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Q. In a closed loop, if the net current is zero, what can be said about the magnetic field according to Ampere's Law?
A.
The magnetic field is zero everywhere
B.
The magnetic field is uniform
C.
The magnetic field can be non-zero
D.
The magnetic field is only zero at the center
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Solution
According to Ampere's Law, if the net current through a closed loop is zero, the line integral of the magnetic field around that loop is also zero, but the magnetic field can still be non-zero in some regions.
Correct Answer: C — The magnetic field can be non-zero
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Q. In a generator, if the speed of rotation is doubled, what happens to the induced EMF?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It becomes zero
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Solution
The induced EMF in a generator is directly proportional to the speed of rotation. Therefore, if the speed is doubled, the induced EMF also doubles.
Correct Answer: A — It doubles
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Q. In a generator, mechanical energy is converted into electrical energy through the principle of:
A.
Electrostatics
B.
Electromagnetic induction
C.
Thermodynamics
D.
Optics
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Solution
In a generator, mechanical energy is converted into electrical energy through the principle of electromagnetic induction, as the motion of conductors in a magnetic field induces an EMF.
Correct Answer: B — Electromagnetic induction
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Q. In a generator, mechanical energy is converted into electrical energy through which principle?
A.
Electromagnetic induction
B.
Thermal conduction
C.
Photoelectric effect
D.
Capacitance
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Solution
In a generator, mechanical energy is converted into electrical energy through the principle of electromagnetic induction.
Correct Answer: A — Electromagnetic induction
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Q. In a generator, mechanical energy is converted into electrical energy through which process?
A.
Electromagnetic induction
B.
Thermal conduction
C.
Photoelectric effect
D.
Electrolysis
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Solution
In a generator, mechanical energy is converted into electrical energy through the process of electromagnetic induction.
Correct Answer: A — Electromagnetic induction
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Q. In a generator, what is the role of the rotating coil in a magnetic field?
A.
To create a magnetic field
B.
To induce current
C.
To store energy
D.
To measure voltage
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Solution
In a generator, the rotating coil in a magnetic field induces current through electromagnetic induction, converting mechanical energy into electrical energy.
Correct Answer: B — To induce current
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Q. In a magnetic field, the force on a charged particle is maximum when the particle's velocity is:
A.
Parallel to the field
B.
Perpendicular to the field
C.
At an angle of 45 degrees
D.
At an angle of 90 degrees
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Solution
The magnetic force on a charged particle is given by F = qvB sin(θ), which is maximum when θ = 90 degrees (perpendicular).
Correct Answer: B — Perpendicular to the field
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