Electromagnetism – 100 Basic MCQs with Answers & Explanations | Board & MDCAT Preparation

100 Important Basic MCQs (Level -1) on Electromagnetism, Physics (Unit-Wise MCQs Practice):

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👉Physics MCQs Hub – Unit wise Physics MCQs Practice (Main-Page)👈

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Whether you are preparing for board examinations, chapter tests, college assessments, or competitive entrance exams (MDCAT, ECAT, NUST, PIEAS, GIKI, UET, FAST, and other engineering or medical admission tests), this comprehensive MCQ collection is designed to help you master Electromagnetism. The questions are arranged progressively—from basic concepts to advanced numerical problems and higher-order thinking—ensuring complete and systematic preparation for every type of examination.

This chapter-wise MCQ collection includes:

• 100 Basic MCQs Level-1 (1–100) – Covering magnetic fields, magnetic force, magnetic flux, Ampere's law, solenoids, galvanometers, transformers, alternating current, and other fundamental concepts.
• 100 Advanced & Numerical MCQs (101–200) – Focusing on formulas, calculations, magnetic fields, force on charges, transformer problems, AC circuits, inductance, and practical applications.
• 50 Higher-Order Thinking Skills (HOTS) MCQs (201–250) – Designed to strengthen analytical reasoning, conceptual understanding, and advanced problem-solving skills.
• 50 Challenging MCQs Quiz with Answers – A carefully selected mix of conceptual, numerical, and HOTS questions for quick revision and self-assessment.

This MCQ collection covers:

• Magnetic fields and magnetic force
• Magnetic flux and Ampere's Law
• Solenoids and current-carrying conductors
• Motion of charged particles in magnetic fields
• Velocity selector and cyclotron
• Torque on current loops and magnetic dipoles
• Galvanometer, ammeter, voltmeter, and multimeter
• Electromagnetic induction and Lenz's Law
• Self and mutual inductance
• Transformers and alternating current (AC)
• Reactance, impedance, resonance, and power factor
• Electromagnetic waves and Maxwell's theory
• Practical applications and measurement techniques

Every MCQ includes the correct answer with a clear, concept-based explanation to strengthen understanding, improve problem-solving skills, and reinforce key physics concepts.

This question bank helps students to:

• Build a strong conceptual foundation
• Improve numerical and analytical skills
• Master electromagnetism formulas and applications
• Avoid common examination mistakes
• Increase speed, accuracy, and confidence
• Prepare effectively for both board and competitive examinations

With 250 carefully selected MCQs arranged into 100 Basic, 100 Advanced & Numerical, and 50 HOTS MCQs, this all-in-one question bank provides complete preparation for Electromagnetism, making it an excellent resource for achieving success in both board examinations and competitive entrance tests.

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Electromagnetism MCQs Level 1 – 100 Basic MCQs (1–100)

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MCQs No. 1

The SI unit of magnetic field is:

a. Tesla
b. Weber
c. Henry
d. Volt

Correct answer: a. Tesla

Explanation: The SI unit of magnetic field (magnetic flux density) is tesla (T). One tesla is equal to one weber per square meter (Wb/m²).

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MCQs No. 2

A charged particle moving parallel to a magnetic field experiences:

a. Maximum force
b. Minimum force
c. Zero force
d. Infinite force

Correct answer: c. Zero force

Explanation: The magnetic force on a moving charge is given by F = qvB sinθ. When the particle moves parallel to the magnetic field, θ = 0°, so sin0° = 0 and the magnetic force becomes zero.

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MCQs No. 3

The magnetic field at the center of a circular coil increases when:

a. The radius is increased
b. The current is decreased
c. The number of turns is increased
d. The distance from the coil is increased

Correct answer: c. The number of turns is increased

Explanation: The magnetic field at the center of a circular coil is directly proportional to the number of turns. More turns produce a stronger magnetic field.

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MCQs No. 4

The magnetic force acting on a moving charge is given by:

a. qE
b. qvB
c. qvB sinθ
d. qEB

Correct answer: c. qvB sinθ

Explanation: The magnetic force depends on the charge, its velocity, the magnetic field strength, and the angle between the velocity and the magnetic field.

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MCQs No. 5

The SI unit of magnetic flux is:

a. Tesla
b. Weber
c. Henry
d. Ohm

Correct answer: b. Weber

Explanation: Magnetic flux is measured in weber (Wb). One weber represents the total magnetic field passing through an area.

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MCQs No. 6

The direction of the magnetic field around a straight current-carrying conductor is determined by:

a. Fleming's Left-Hand Rule
b. Fleming's Right-Hand Rule
c. Right-Hand Thumb Rule
d. Lenz's Law

Correct answer: c. Right-Hand Thumb Rule

Explanation: According to the Right-Hand Thumb Rule, if the thumb points in the direction of current, the curled fingers indicate the direction of the magnetic field.

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MCQs No. 7

Two parallel conductors carrying currents in the same direction:

a. Repel each other
b. Attract each other
c. Remain unaffected
d. Rotate about each other

Correct answer: b. Attract each other

Explanation: Parallel currents flowing in the same direction produce attractive magnetic forces, whereas currents in opposite directions repel each other.

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MCQs No. 8

Torque on a magnetic dipole is maximum when the angle between the magnetic moment and magnetic field is:

a. 0°
b. 30°
c. 60°
d. 90°

Correct answer: d. 90°

Explanation: Torque is given by τ = mB sinθ. Since sin90° = 1, the torque is maximum when the magnetic moment is perpendicular to the magnetic field.

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MCQs No. 9

The magnetic dipole moment of a current-carrying coil is:

a. IA
b. NIA
c. NI
d. BA

Correct answer: b. NIA

Explanation: The magnetic dipole moment of a coil is m = NIA, where N is the number of turns, I is the current, and A is the area of the coil.

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MCQs No. 10

The SI unit of magnetic dipole moment is:

a. A/m
b. J/T
c. T/m
d. Weber

Correct answer: b. J/T

Explanation: The SI unit of magnetic dipole moment is joule per tesla (J/T), which is equivalent to ampere square metre (A·m²).

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MCQs No. 11

According to Faraday's law, induced emf depends upon:

a. Magnetic flux
b. Rate of change of magnetic flux
c. Current
d. Resistance

Correct answer: b. Rate of change of magnetic flux

Explanation: Faraday's law states that the magnitude of induced emf is directly proportional to the rate at which magnetic flux changes through a circuit.

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MCQs No. 12

The negative sign in Faraday's law represents:

a. Energy loss
b. Current direction
c. Lenz's law
d. Resistance

Correct answer: c. Lenz's law

Explanation: The negative sign indicates that the induced emf always opposes the change in magnetic flux that produces it, as stated by Lenz's law.

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MCQs No. 13

The SI unit of self-inductance is:

a. Tesla
b. Weber
c. Henry
d. Volt

Correct answer: c. Henry

Explanation: Self-inductance is measured in henry (H). A coil has an inductance of one henry if a current changing at one ampere per second induces one volt of emf.

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MCQs No. 14

Back emf is produced in a:

a. Resistor
b. Capacitor
c. Inductor
d. Battery

Correct answer: c. Inductor

Explanation: An inductor produces a back emf whenever the current through it changes. This induced emf opposes the change in current.

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MCQs No. 15

A transformer operates only with:

a. Direct current
b. Alternating current
c. Both AC and DC
d. None of these

Correct answer: b. Alternating current

Explanation: A transformer requires a continuously changing magnetic flux, which is produced only by alternating current (AC).

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MCQs No. 16

A step-up transformer increases:

a. Current
b. Voltage
c. Power
d. Resistance

Correct answer: b. Voltage

Explanation: A step-up transformer increases the output voltage while reducing the output current, keeping power nearly constant in an ideal transformer.

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MCQs No. 17

The standard frequency of AC supply in Pakistan is:

a. 40 Hz
b. 50 Hz
c. 60 Hz
d. 100 Hz

Correct answer: b. 50 Hz

Explanation: The national electricity supply in Pakistan operates at a frequency of 50 hertz (Hz).

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MCQs No. 18

The average value of alternating current over one complete cycle is:

a. Maximum
b. Zero
c. RMS value
d. Peak value

Correct answer: b. Zero

Explanation: During one complete cycle, the positive and negative halves of alternating current are equal in magnitude and opposite in direction, giving an average value of zero.

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MCQs No. 19

The RMS value of alternating current is:

a. I₀
b. I₀/√2
c. √2 I₀
d. I₀/2

Correct answer: b. I₀/√2

Explanation: The RMS (root mean square) value of alternating current is equal to the peak current divided by √2 and represents the equivalent DC current producing the same heating effect.

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MCQs No. 20

The power factor of an AC circuit is equal to:

a. sinφ
b. cosφ
c. tanφ
d. secφ

Correct answer: b. cosφ

Explanation: The power factor is the cosine of the phase angle between voltage and current. A higher power factor indicates more efficient use of electrical power.

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MCQs No. 21

The magnetic field at a distance r from a long straight conductor carrying current I is:

a. μ₀I/2πr
b. μ₀Ir/2π
c. μ₀/2πIr
d. 2πr/μ₀I

Correct answer: a. μ₀I/2πr

Explanation: According to Ampère's law, the magnetic field around a long straight conductor is directly proportional to the current and inversely proportional to the distance from the conductor.

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MCQs No. 22

If the current through a conductor is doubled, the magnetic field becomes:

a. Unchanged
b. Half
c. Double
d. Four times

Correct answer: c. Double

Explanation: Since B ∝ I, doubling the current also doubles the magnetic field produced around the conductor.

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MCQs No. 23

The radius of the circular path of a charged particle moving in a magnetic field is directly proportional to:

a. Charge
b. Magnetic field strength
c. Velocity
d. Inverse of velocity

Correct answer: c. Velocity

Explanation: The radius is given by r = mv/qB. Therefore, increasing the particle's velocity increases the radius of its circular path.

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MCQs No. 24

A magnetic force acting on a charged particle does not change its:

a. Speed
b. Direction of motion
c. Momentum direction
d. Kinetic energy

Correct answer: d. Kinetic energy

Explanation: Since the magnetic force always acts perpendicular to the velocity, it changes only the direction of motion and does no work. Therefore, the kinetic energy remains constant.

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MCQs No. 25

The SI unit of magnetic permeability is:

a. Tesla
b. Henry per metre (H/m)
c. Weber
d. Ampere

Correct answer: b. Henry per metre (H/m)

Explanation: Magnetic permeability measures how easily a material allows magnetic field lines to pass through it. Its SI unit is henry per metre (H/m).

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MCQs No. 26

Force per unit length between two parallel current-carrying conductors is used to define the:

a. Tesla

b. Ampere

c. Volt

d. Ohm

Correct answer: b

Explanation: The SI unit of electric current, ampere, was historically defined in terms of the force per unit length between two long parallel conductors carrying equal currents.

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MCQs No. 27

The torque on a rectangular current-carrying coil depends upon:

a. Area of the coil

b. Current through the coil

c. Magnetic field strength

d. All of these

Correct answer: d

Explanation: The torque on a current-carrying coil is given by

$$\tau = NIAB\sin\theta$$

It depends on the number of turns (N), current (I), area (A), magnetic field (B), and the angle (θ).

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MCQs No. 28

A moving-coil galvanometer converts electrical energy into:

a. Heat energy

b. Light energy

c. Mechanical motion

d. Sound energy

Correct answer: c

Explanation: When current passes through the galvanometer coil, it experiences a magnetic torque that rotates the coil and moves the pointer, converting electrical energy into mechanical motion.

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MCQs No. 29

The sensitivity of a galvanometer can be increased by:

a. Increasing the magnetic field strength

b. Decreasing the number of turns

c. Increasing the spring constant

d. Decreasing the coil area

Correct answer: a

Explanation: A stronger magnetic field produces a greater torque for the same current, making the galvanometer more sensitive.

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MCQs No. 30

To convert a galvanometer into an ammeter, a ________ resistance is connected with it.

a. High series

b. Low parallel

c. High parallel

d. Low series

Correct answer: b

Explanation: A low-value shunt resistance is connected in parallel with the galvanometer so that most of the current bypasses the delicate coil.

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MCQs No. 31

To convert a galvanometer into a voltmeter, a ________ resistance is connected with it.

a. Low series

b. High parallel

c. High series

d. Low parallel

Correct answer: c

Explanation: A high resistance is connected in series with the galvanometer to limit the current passing through it.

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MCQs No. 32

Induced emf is maximum when the magnetic flux changes:

a. Very slowly

b. At a constant value

c. At the greatest rate

d. Becomes zero

Correct answer: c

Explanation: According to Faraday's law,

$$e=-\frac{d\Phi}{dt}$$

the induced emf is directly proportional to the rate of change of magnetic flux.

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MCQs No. 33

When a magnet approaches a coil, the induced current produced in the coil:

a. Assists the motion of the magnet

b. Opposes the motion of the magnet

c. Stops immediately

d. Has no effect

Correct answer: b

Explanation: According to Lenz's law, the induced current always opposes the change in magnetic flux that produces it.

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MCQs No. 34

The SI unit of mutual inductance is:

a. Tesla

b. Weber

c. Henry

d. Volt

Correct answer: c

Explanation: Both self-inductance and mutual inductance are measured in henry (H).

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MCQs No. 35

The energy stored in an inductor is given by:

a. $LI^2$

b. $I^2/L$

c. $\frac{1}{2}LI^2$

d. $L/I^2$

Correct answer: c

Explanation: The energy stored in the magnetic field of an inductor is

$$U=\frac{1}{2}LI^2$$

where L is the inductance and I is the current.

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MCQs No. 36

Back emf produced in an inductor is proportional to the:

a. Current

b. Resistance

c. Rate of change of current

d. Applied voltage

Correct answer: c

Explanation: Back emf is given by

$$e=-L\frac{di}{dt}$$

It depends on how rapidly the current changes.

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MCQs No. 37

In an RL circuit, the current increases:

a. Instantly

b. Linearly

c. Exponentially

d. Randomly

Correct answer: c

Explanation: Due to self-inductance, the current in an RL circuit increases exponentially until it reaches its maximum value.

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MCQs No. 38

The time constant of an RL circuit is:

a. $R/L$

b. $L/R$

c. $RC$

d. $1/RC$

Correct answer: b

Explanation: The time constant is

$$\tau=\frac{L}{R}$$

It represents the time required for the current to reach about 63% of its final value.

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MCQs No. 39

The laminated iron core of a transformer is used to reduce:

a. Copper loss

b. Hysteresis loss

c. Eddy current loss

d. Leakage flux

Correct answer: c

Explanation: Laminating the iron core breaks the paths of circulating eddy currents, thereby reducing energy losses.

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MCQs No. 40

In an ideal transformer, the input power is ________ the output power.

a. Greater than

b. Less than

c. Equal to

d. Twice

Correct answer: c

Explanation: An ideal transformer has no energy losses. Therefore,

$$P_{\text{input}}=P_{\text{output}}$$

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MCQs No. 41

An AC generator works on the principle of:

a. Coulomb's law

b. Faraday's law of electromagnetic induction

c. Ohm's law

d. Ampere's law

Correct answer: b

Explanation: An AC generator converts mechanical energy into electrical energy by electromagnetic induction according to Faraday's law.

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MCQs No. 42

The peak value of an alternating current is related to its RMS value by:

a. $I_0=\sqrt2\,I_{\rm rms}$

b. $I_0=I_{\rm rms}/\sqrt2$

c. $I_0=2I_{\rm rms}$

d. $I_0=I_{\rm rms}/2$

Correct answer: a

Explanation: The relationship between peak and RMS current is

$$I_0=\sqrt2\,I_{\rm rms}$$

Similarly,

$$V_0=\sqrt2\,V_{\rm rms}$$

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MCQs No. 43

In a purely resistive AC circuit, the current and voltage are:

a. 90° out of phase

b. 180° out of phase

c. In the same phase

d. 45° out of phase

Correct answer: c

Explanation: In a purely resistive circuit, the current reaches its maximum and minimum values at the same time as the voltage.

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MCQs No. 44

The capacitive reactance is given by:

a. $X_C=\omega C$

b. $X_C=\frac1{\omega C}$

c. $X_C=\omega L$

d. $X_C=\frac{L}{\omega}$

Correct answer: b

Explanation: Capacitive reactance is

$$X_C=\frac1{\omega C}$$

It decreases as the frequency increases.

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MCQs No. 45

The inductive reactance is given by:

a. $X_L=\omega L$

b. $X_L=\frac1{\omega L}$

c. $X_L=\omega C$

d. $X_L=\frac1{\omega C}$

Correct answer: a

Explanation: Inductive reactance is

$$X_L=\omega L$$

It increases directly with frequency.

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MCQs No. 46

The SI unit of impedance is:

a. Henry

b. Tesla

c. Ohm

d. Weber

Correct answer: c

Explanation: Impedance is the total opposition offered to alternating current and is measured in ohm (Ω).

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MCQs No. 47

The power factor of an AC circuit is equal to:

a. sin φ

b. cos φ

c. tan φ

d. sec φ

Correct answer: b

Explanation: Power factor is defined as

$$\text{Power Factor}=\cos\phi$$

where φ is the phase angle between voltage and current.

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MCQs No. 48

Electrical resonance in an LC circuit occurs when:

a. $X_L=X_C$

b. $X_L>X_C$

c. $X_L<X_C$

d. $R=0$

Correct answer: a

Explanation: At resonance, the inductive reactance equals the capacitive reactance. The two reactances cancel each other, making the circuit purely resistive.

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MCQs No. 49

The frequency of oscillation in an LC circuit is:

a. $\frac1{LC}$

b. $\frac1{2\pi\sqrt{LC}}$

c. $\sqrt{LC}$

d. $2\pi\sqrt{LC}$

Correct answer: b

Explanation: The resonant frequency of an LC circuit is

$$f=\frac1{2\pi\sqrt{LC}}$$

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MCQs No. 50

At resonance in a series RLC circuit, the impedance is:

a. Maximum

b. Infinite

c. Minimum

d. Zero

Correct answer: c

Explanation: At resonance, the inductive and capacitive reactances are equal and cancel each other. Therefore, the impedance becomes minimum and is equal to the resistance of the circuit.

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MCQs No. 51

Eddy currents can be reduced by using:

a. Thick iron core
b. Solid copper core
c. Laminated iron core
d. Aluminum core

Correct answer: c

Explanation: Laminating the iron core breaks the paths of eddy currents, thereby reducing energy losses due to heating.

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MCQs No. 52

Cyclotron frequency depends upon:

a. Velocity of particle
b. Radius of circular path
c. Magnetic field strength
d. Time of revolution

Correct answer: c

Explanation: Cyclotron frequency is given by f = qB/2πm, so it depends on the magnetic field and the particle's charge-to-mass ratio.

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MCQs No. 53

A charged particle moving perpendicular to a uniform magnetic field follows:

a. Straight-line motion
b. Circular motion
c. Parabolic motion
d. Random motion

Correct answer: b

Explanation: The magnetic force always acts perpendicular to the velocity, providing the required centripetal force for circular motion.

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MCQs No. 54

If the velocity of a charged particle is exactly perpendicular to the magnetic field, the path will be:

a. Linear
b. Spiral
c. Circular
d. Elliptical

Correct answer: c

Explanation: With no velocity component parallel to the field, the particle undergoes uniform circular motion.

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MCQs No. 55

If a charged particle has both parallel and perpendicular velocity components in a magnetic field, it follows:

a. Circular path
b. Helical path
c. Straight path
d. Elliptical path

Correct answer: b

Explanation: The perpendicular component causes circular motion, while the parallel component produces uniform forward motion, resulting in a helix.

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MCQs No. 56

The magnetic field inside a long solenoid is:

a. Zero
b. Non-uniform
c. Nearly uniform
d. Random

Correct answer: c

Explanation: Inside a long solenoid, the magnetic field is strong and almost uniform because the field lines are parallel and equally spaced.

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MCQs No. 57

The magnetic field outside a long solenoid is:

a. Very strong
b. Uniform
c. Nearly zero
d. Infinite

Correct answer: c

Explanation: Outside a long solenoid, the magnetic field is very weak because most field lines remain confined inside the solenoid.

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MCQs No. 58

Electromagnetic waves consist of:

a. Electric field only
b. Magnetic field only
c. Electric and magnetic fields
d. Charged particles only

Correct answer: c

Explanation: Electromagnetic waves consist of oscillating electric and magnetic fields that are mutually perpendicular.

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MCQs No. 59

In an electromagnetic wave, the electric field and magnetic field are:

a. Parallel
b. Opposite
c. Perpendicular to each other
d. At 45° to each other

Correct answer: c

Explanation: The electric field, magnetic field, and direction of propagation are all mutually perpendicular.

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MCQs No. 60

The speed of electromagnetic waves in vacuum is:

a. 3 × 10⁶ m/s
b. 3 × 10⁸ m/s
c. 3 × 10¹⁰ m/s
d. 3 × 10⁴ m/s

Correct answer: b

Explanation: Electromagnetic waves travel through vacuum at the speed of light, 3 × 10⁸ m/s.

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MCQs No. 61

Electromagnetic waves carry:

a. Charge only
b. Mass only
c. Energy and momentum
d. Electric current

Correct answer: c

Explanation: Electromagnetic waves transfer both energy and momentum from one place to another.

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MCQs No. 62

The Poynting vector represents:

a. Electric field strength
b. Magnetic field strength
c. Direction of energy flow
d. Electric charge density

Correct answer: c

Explanation: The Poynting vector gives both the direction and rate of electromagnetic energy transfer.

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MCQs No. 63

The SI unit of the Poynting vector is:

a. W/m²
b. J/m²
c. T/m²
d. V/m

Correct answer: a

Explanation: The Poynting vector measures power transmitted per unit area, so its SI unit is watt per square meter.

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MCQs No. 64

The symbol used for magnetic susceptibility is:

a. μ
b. χ
c. ε
d. σ

Correct answer: b

Explanation: Magnetic susceptibility is represented by the Greek letter χ (chi).

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MCQs No. 65

Diamagnetic materials are:

a. Strongly attracted by magnetic fields
b. Weakly repelled by magnetic fields
c. Strongly repelled by magnetic fields
d. Completely unaffected by magnetic fields

Correct answer: b

Explanation: Diamagnetic materials develop an induced magnetic field opposite to the applied field and are weakly repelled.

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MCQs No. 66

Paramagnetic materials are:

a. Strongly attracted by magnetic fields
b. Weakly attracted by magnetic fields
c. Strongly repelled by magnetic fields
d. Not affected by magnetic fields

Correct answer: b

Explanation: Paramagnetic materials have a small positive susceptibility and are weakly attracted by external magnetic fields.

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MCQs No. 67

Ferromagnetic materials exhibit:

a. No magnetism
b. Weak magnetism
c. Strong magnetism
d. Temporary electric charge

Correct answer: c

Explanation: Ferromagnetic materials contain magnetic domains that align strongly in an external magnetic field.

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MCQs No. 68

A hysteresis loop represents the relationship between:

a. Magnetic flux density (B) and magnetic field strength (H)
b. Voltage and current
c. Electric field and magnetic field
d. Current and resistance

Correct answer: a

Explanation: A hysteresis curve shows how magnetic flux density varies with the magnetizing field.

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MCQs No. 69

Retentivity of a magnetic material refers to its ability to:

a. Resist electric current
b. Retain magnetism after the external field is removed
c. Conduct electricity
d. Increase magnetic permeability

Correct answer: b

Explanation: Retentivity is the ability of a material to remain magnetized after the magnetizing force has been removed.

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MCQs No. 70

Coercivity is the:

a. Maximum magnetic field produced
b. Reverse magnetic field required to demagnetize a material
c. Electrical resistance of a magnet
d. Magnetic flux through a coil

Correct answer: b

Explanation: Coercivity is the magnitude of the reverse magnetic field needed to reduce the residual magnetism to zero.

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MCQs No. 71

Soft iron is commonly used for transformer cores because it has:

a. High coercivity
b. Low retentivity
c. High electrical resistance
d. Low permeability

Correct answer: b

Explanation: Soft iron is easily magnetized and demagnetized, making it ideal for transformer cores.

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MCQs No. 72

Hard steel is preferred for permanent magnets because it has:

a. Low coercivity
b. High retentivity
c. Low permeability
d. Low magnetic susceptibility

Correct answer: b

Explanation: Hard steel retains its magnetism for a long time due to its high retentivity and coercivity.

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MCQs No. 73

The symbol used for magnetic flux density is:

a. Φ
b. B
c. H
d. μ

Correct answer: b

Explanation: Magnetic flux density is represented by B and is measured in tesla.

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MCQs No. 74

Magnetic flux through a surface is given by:

a. BA
b. B/A
c. A/B
d. B²A

Correct answer: a

Explanation: When the magnetic field is perpendicular to the surface, magnetic flux is Φ = BA.

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MCQs No. 75

The SI unit of magnetic field strength (H) is:

a. Tesla
b. Ampere per meter (A/m)
c. Weber
d. Henry

Correct answer: b

Explanation: Magnetic field strength (H) is measured in ampere per meter (A/m).

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MCQs No. 76

When the magnetic flux linked with a coil is maximum, the induced emf is:

a. Maximum
b. Minimum
c. Zero
d. Infinite

Correct answer: c

Explanation: According to Faraday's law, induced emf depends on the rate of change of magnetic flux, not on the flux itself. When the flux is maximum (momentarily constant), its rate of change is zero, so the induced emf is zero.

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MCQs No. 77

Laminated iron cores are used in transformers to reduce:

a. Magnetic flux
b. Eddy currents
c. Resistance
d. Voltage

Correct answer: b

Explanation: Thin insulated laminations interrupt the paths of circulating eddy currents, thereby minimizing heating and power loss.

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MCQs No. 78

When a conductor moves through a magnetic field, it produces:

a. Resistance
b. Heat
c. Induced emf
d. Light

Correct answer: c

Explanation: Motion of a conductor across magnetic field lines changes magnetic flux and induces an emf according to Faraday's law.

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MCQs No. 79

The direction of the induced current is determined by:

a. Fleming's Left-Hand Rule
b. Fleming's Right-Hand Rule
c. Lenz's Law
d. Ampere's Law

Correct answer: c

Explanation: Lenz's law states that the induced current always flows in a direction that opposes the change producing it.

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MCQs No. 80

EMI stands for:

a. Electric Motion Induction
b. Electromagnetic Induction
c. Energy Magnetic Interaction
d. Electric Mass Inertia

Correct answer: b

Explanation: EMI is the abbreviation for Electromagnetic Induction, the production of emf due to changing magnetic flux.

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MCQs No. 81

If the area of a coil is doubled while other factors remain constant, the induced emf becomes:

a. Half
b. Same
c. Double
d. Zero

Correct answer: c

Explanation: Since magnetic flux is proportional to the area of the coil, doubling the area doubles the induced emf when the magnetic field changes.

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MCQs No. 82

Self-inductance of a coil depends on:

a. Shape and dimensions of the coil
b. Number of turns
c. Core material
d. All of these

Correct answer: d

Explanation: Self-inductance depends on the geometry of the coil, the number of turns, and the magnetic permeability of the core material.

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MCQs No. 83

Back emf in an inductor always:

a. Assists the applied voltage
b. Opposes the applied voltage
c. Increases the current instantly
d. Stops the circuit permanently

Correct answer: b

Explanation: Back emf is produced according to Lenz's law and always opposes the change in current responsible for its production.

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MCQs No. 84

Reactance is the opposition offered to:

a. Direct current (DC)
b. Alternating current (AC)
c. Both AC and DC equally
d. Static electricity

Correct answer: b

Explanation: Reactance is offered by inductors and capacitors only in AC circuits because it depends on frequency.

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MCQs No. 85

At very high frequency, a capacitor behaves like:

a. An open circuit
b. A short circuit
c. A resistor
d. An inductor

Correct answer: b

Explanation: Capacitive reactance decreases as frequency increases, allowing current to pass more easily.

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MCQs No. 86

At very high frequency, an inductor behaves like:

a. A short circuit
b. An open circuit
c. A capacitor
d. A resistor

Correct answer: b

Explanation: Inductive reactance increases with frequency, so an inductor strongly opposes AC at high frequencies.

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MCQs No. 87

The average power consumed in a purely inductive AC circuit is:

a. Maximum
b. Minimum
c. Zero
d. Infinite

Correct answer: c

Explanation: In a purely inductive circuit, current lags voltage by 90°, making the average power over one complete cycle zero.

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MCQs No. 88

The average power consumed in a purely capacitive AC circuit is:

a. Zero
b. Maximum
c. Large
d. Infinite

Correct answer: a

Explanation: In a purely capacitive circuit, current leads voltage by 90°, so the average power consumed is zero.

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MCQs No. 89

A transformer cannot operate on direct current because:

a. It has high resistance
b. There is no changing magnetic flux
c. It requires low voltage only
d. It draws excessive current only

Correct answer: b

Explanation: A transformer works on electromagnetic induction, which requires a changing magnetic flux. DC produces constant flux.

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MCQs No. 90

The scientist who unified electricity and magnetism into one theory was:

a. Charles Coulomb
b. Michael Faraday
c. James Clerk Maxwell
d. André-Marie Ampère

Correct answer: c

Explanation: James Clerk Maxwell developed Maxwell's equations, providing the unified theory of electromagnetism.

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MCQs No. 91

The energy stored in an inductor is proportional to:

a. Current
b. Square of current
c. Resistance
d. Voltage only

Correct answer: b

Explanation: The energy stored in an inductor is given by U = ½LI², so it is proportional to the square of the current.

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MCQs No. 92

Eddy currents are responsible for:

a. Heating effect
b. Magnetic damping
c. Energy loss in electrical machines
d. All of these

Correct answer: d

Explanation: Eddy currents produce heating, cause magnetic damping, and reduce the efficiency of transformers and motors.

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MCQs No. 93

A cyclotron accelerates charged particles using:

a. Electric field only
b. Magnetic field only
c. Both electric and magnetic fields
d. Gravitational field

Correct answer: c

Explanation: The magnetic field keeps the particles in circular paths, while the electric field accelerates them across the gap.

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MCQs No. 94

The SI unit of impedance is:

a. Ohm (Ω)
b. Henry (H)
c. Tesla (T)
d. Weber (Wb)

Correct answer: a

Explanation: Impedance is the total opposition offered to AC and is measured in ohms.

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MCQs No. 95

In a purely inductive AC circuit, the phase difference between voltage and current is:

a. 0°
b. 45°
c. 90°
d. 180°

Correct answer: c

Explanation: In an ideal inductive circuit, current lags the voltage by 90°.

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MCQs No. 96

In a purely capacitive AC circuit:

a. Current leads voltage by 90°
b. Voltage leads current by 90°
c. Current and voltage are in phase
d. No current flows

Correct answer: a

Explanation: In a purely capacitive circuit, current reaches its maximum before the voltage by a phase angle of 90°.

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MCQs No. 97

The frequency of oscillations in an LC circuit depends on:

a. Resistance only
b. Inductance only
c. Capacitance only
d. Both inductance and capacitance

Correct answer: d

Explanation: The oscillation frequency is f = 1/2π√LC, so it depends on both L and C.

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MCQs No. 98

The magnetic permeability of free space is represented by:

a. μ₀
b. ε₀
c. χ
d. σ

Correct answer: a

Explanation: μ₀ denotes the permeability of free space and has the value 4π × 10⁻⁷ H/m.

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MCQs No. 99

The speed of electromagnetic waves in a medium is given by:

a. $v=\frac{1}{\sqrt{\mu\varepsilon}}$
b. $v=\frac{\mu}{\varepsilon}$
c. $v=\mu\varepsilon$
d. $v=\sqrt{\mu\varepsilon}$

Correct answer: a

Explanation: The speed of electromagnetic waves depends on the permeability (μ) and permittivity (ε) of the medium and is given by $v=\frac{1}{\sqrt{\mu\varepsilon}}$

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MCQs No. 100

The complete theory of electromagnetism was established by:

a. Michael Faraday
b. André-Marie Ampère
c. James Clerk Maxwell
d. Nikola Tesla

Correct answer: c

Explanation: James Clerk Maxwell formulated the four Maxwell's equations, which unified electricity, magnetism, and electromagnetic waves into a single theory.

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