Electromagnetic Theory MCQ Quiz - Objective Question with Answer for Electromagnetic Theory - Download Free PDF
Last updated on Jul 9, 2025
Latest Electromagnetic Theory MCQ Objective Questions
Electromagnetic Theory Question 1:
Answer (Detailed Solution Below)
Electromagnetic Theory Question 1 Detailed Solution
Calculation:
In a plane electromagnetic wave:
E, B, and the direction of propagation are mutually perpendicular.
The direction of B is determined using the right-hand rule: E × B = direction of wave.
Direction of wave propagation: +x
Electric field E direction: +z
To satisfy +z × ? = +x, the correct direction for B is -y.
Correct Option: (4)
Electromagnetic Theory Question 2:
What is the characteristic impedance of a lossless transmission line having inductance of 100nH/m and capacitance of 40pF/m.
Answer (Detailed Solution Below)
Electromagnetic Theory Question 2 Detailed Solution
Concept:
The characteristic impedance
Where,
= Inductance per unit length (in H/m) = Capacitance per unit length (in F/m)
Given:
Calculation:
Hence, the correct answer is 3
Electromagnetic Theory Question 3:
A lossless transmission line is terminated in a load resulting in VSWR of 1.5. If 50 W is the incident power on the load, what is the reflected power?
Answer (Detailed Solution Below)
Electromagnetic Theory Question 3 Detailed Solution
The VSWR is mathematically related to the reflection coefficient (Γ), which quantifies the fraction of incident power reflected back due to impedance mismatch between the transmission line and the load. The reflection coefficient is given by:
Γ = (VSWR - 1) / (VSWR + 1)
Given in the problem:
- VSWR = 1.5
- Incident power = 50 W
Step 1: Calculate the Reflection Coefficient (Γ):
Substitute the given VSWR value into the formula:
Γ = (1.5 - 1) / (1.5 + 1)
Γ = 0.5 / 2.5
Γ = 0.2
Step 2: Calculate the Reflected Power:
The reflected power (Preflected) can be calculated using the relation:
Preflected = Γ² × Pincident
Substitute the values:
Preflected = (0.2)² × 50
Preflected = 0.04 × 50
Preflected = 2 W
Correct Answer:
The reflected power is 2 W, which corresponds to Option 2.
Electromagnetic Theory Question 4:
In a composite magnetic circuit with two magnetic materials having different permeabilities μ1 and μ2, the total reluctance of the circuit is:
Answer (Detailed Solution Below)
Electromagnetic Theory Question 4 Detailed Solution
Composite Magnetic Circuit with Two Magnetic Materials
Introduction: In a composite magnetic circuit, the circuit consists of different magnetic materials with varying permeabilities (μ1 and μ2). Each material in the circuit contributes to the total reluctance of the system. Reluctance is the magnetic equivalent of electrical resistance and is inversely proportional to the permeability of the material.
Total Reluctance in a Composite Magnetic Circuit:
The total reluctance of a composite magnetic circuit is analogous to the total resistance in an electrical circuit. When magnetic materials with different permeabilities are combined, the overall reluctance of the circuit is determined by summing up the reluctances of each material. This is because the magnetic flux travels through each material sequentially, similar to a series electrical circuit. Mathematically, the total reluctance Rtotal in a composite magnetic circuit is given by:
Rtotal = R1 + R2 + ... + Rn
Where:
- Ri represents the reluctance of the i-th material.
The reluctance of a magnetic material is calculated using the formula:
R = l / (μ * A)
Where:
- R = Reluctance of the material (measured in Ampere-Turns per Weber, A·T/Wb)
- l = Length of the magnetic path through the material (in meters)
- μ = Permeability of the material (in Henrys per meter, H/m)
- A = Cross-sectional area of the material (in square meters)
Since reluctance is inversely proportional to permeability, a material with higher permeability will have lower reluctance, and vice versa. In a composite magnetic circuit, the reluctances of all the materials are added together to determine the total reluctance of the circuit.
Correct Option Analysis:
The correct option is:
Option 3: The sum of reluctances of each material.
This option correctly describes the calculation of total reluctance in a composite magnetic circuit. When multiple materials with different permeabilities are present in the circuit, their reluctances are added together to determine the total reluctance of the circuit. The summation approach is justified because the magnetic flux travels sequentially through each material, and the reluctances act like resistances in a series electrical circuit.
Electromagnetic Theory Question 5:
Which of the following artificial magnets is best suited for use in electrical motors and transformers due to its high efficiency and stable magnetic field?
Answer (Detailed Solution Below)
Electromagnetic Theory Question 5 Detailed Solution
Explanation:
Artificial magnets are man-made magnets, specifically designed and manufactured to possess desired magnetic properties. These magnets are utilized in various applications, including electrical motors, transformers, sensors, and other devices that rely on magnetic fields for operation. Their efficiency, stability, and durability are critical factors in determining their suitability for specific applications.
Correct Option Analysis:
The correct option is:
Option 1: Ceramic Magnet
Ceramic magnets, also known as ferrite magnets, are the best-suited artificial magnets for use in electrical motors and transformers due to their high efficiency and stable magnetic field. These magnets are composed of a ceramic material that includes iron oxide combined with other elements such as barium or strontium. They are widely recognized for their excellent magnetic properties, cost-effectiveness, and versatility in various applications.
Key Features of Ceramic Magnets:
- High Stability: Ceramic magnets exhibit a stable magnetic field over time, making them ideal for applications where consistency is crucial, such as in electrical motors and transformers.
- Resistant to Demagnetization: These magnets are highly resistant to demagnetization, ensuring long-term reliability in demanding environments.
- Cost-Effective: Ceramic magnets are relatively inexpensive to produce, making them an economical choice for industrial applications.
- Wide Operating Temperature Range: They can operate effectively over a broad temperature range without significant loss of magnetic properties.
- Corrosion Resistance: Ceramic magnets are resistant to corrosion, allowing them to function efficiently in various environmental conditions.
Top Electromagnetic Theory MCQ Objective Questions
Electric flux is a _______ field, and its density is a _______ field.
Answer (Detailed Solution Below)
Electromagnetic Theory Question 6 Detailed Solution
Download Solution PDFConcept:
Electric Flux:
- It is defined as the number of electric field lines associated with an area element.
- Electric flux is a scalar quantity, because it's the dot product of two vector quantities, electric field and the perpendicular differential area.
ϕ = E.A = EA cosθ - The SI unit of the electric flux is N-m2/C.
Electric flux density (D) is a vector quantity because it is simply the product of the vector quantity electric field and the scalar quantity permittivity of the medium, i.e.
Its unit is Coulomb per square meter.
The thumb in Fleming's left hand rule indicate:
Answer (Detailed Solution Below)
Electromagnetic Theory Question 7 Detailed Solution
Download Solution PDFCONCEPT:
- Fleming's Left-hand rule gives the force experienced by a charged particle moving in a magnetic field or a current-carrying wire placed in a magnetic field.
- It states that "stretch the thumb, the forefinger, and the central finger of the left hand so that they are mutually perpendicular to each other.
- If the forefinger points in the direction of the magnetic field, the central finger points in the direction of motion of charge, then the thumb points in the direction of force experienced by positively charged particles."
EXPLANATION:
- According to question
- Forefinger (Index finger): Represents the direction of the magnetic field (magnetic flux). Therefore option 3 is correct.
- Middle finger: Represents the direction of motion of charge (current).
- The thumb : Represents the direction of force or motion experienced by positively charged particles.
1 Tesla = _______ Weber/m2
Answer (Detailed Solution Below)
Electromagnetic Theory Question 8 Detailed Solution
Download Solution PDFCONCEPT:
- Magnetic field strength or magnetic field induction or flux density of the magnetic field is equal to the force experienced by a unit positive charge moving with unit velocity in a direction perpendicular to the magnetic field.
- The SI unit of the magnetic field (B) is weber/meter2 (Wbm-2) or tesla.
- The CGS unit of B is gauss.
1 gauss = 10-4 tesla.
EXPLANATION:
- From the above explanation, we can see that the relation between tesla and Weber/m2 is given by:
1 tesla = 1 Weber/m2
The force between two charges is 200 N. If the distance between the charges is doubled, the force will be _______.
Answer (Detailed Solution Below)
Electromagnetic Theory Question 9 Detailed Solution
Download Solution PDFConcept:
Coulomb's law:
It states that the magnitude of the electrostatic force F between two point charges q1 and q2 is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance r between them.
- It is represented mathematically by the equation:
Where ϵ0 is the permittivity of free space (8.854 × 10-12 C2 N-1 m-2).
The value of
Calculation:
So, initial the force between two charges q1 and q2 is 200 N.
If new distance r' = 2 r
New Force is
From (1) and (2)
or
So, the correct option is 50 N.
In the magnetic circuit shown below, what is the flux density produced if the relative permeability of the core material under the given condition is 1000?
Answer (Detailed Solution Below)
Electromagnetic Theory Question 10 Detailed Solution
Download Solution PDFConcept:
Magnetic Field Strength (H): the amount of magnetizing force required to create a certain field density in certain magnetic material per unit length.
The intensity of Magnetization (I): It is induced pole strength developed per unit area inside the magnetic material.
The net Magnetic Field Density (Bnet) inside the magnetic material is due to:
- Internal factor (I)
- External factor (H)
∴ Bnet ∝ (H + I)
Bnet = μ0(H + I) …. (1)
Where μ0 is absolute permeability.
Note: More external factor (H) causes more internal factor (I).
∴ I ∝ H
I = KH …. (2)
And K is the susceptibility of magnetic material.
From equation (1) and equation (2):
Bnet = μ0(H + KH)
Bnet = μ0H(1 + K) …. (3)
Dividing equation (3) by H on both side
or, μ0μr = μ0(1 + K)
∴ μr = (1 + K) .... (4)
From equation (3) and (4)
Bnet = μ0μrH
Calculation:
Given Magnetic Circuit,
N = 100
I = 5 A
L = 2πr = 2π × 5 × 10-2 m
From above concept,
We know that,
Bnet = μ0μrH
And, μr = 1000
Find H = ___________ A/m at the center of a circular coil of diameter 1 m and carrying a current of 2 A.
Answer (Detailed Solution Below)
Electromagnetic Theory Question 11 Detailed Solution
Download Solution PDFConcept:
The magnetic field intensity (H) of a circular coil is given by
Where I is the current flow through the coil
R is the radius of the circular coil
Calculation:
Given that, Current (I) = 2 A
Diameter = 1 m
Radius (R) = 0.5 m
Magnetic field intensity
Common Mistake:
The magnetic field intensity (H) of a circular coil is given by
Consider the following statements:
The force per unit length between two stationary parallel wires carrying (steady) currents _____.
A. is inversely proportional to the separation of wires
B. is proportional to the magnitude of each current
C. satisfies Newton's third law
Out of this _____.Answer (Detailed Solution Below)
Electromagnetic Theory Question 12 Detailed Solution
Download Solution PDFThe force between two current-carrying parallel conductors:
- Two current-carrying conductors attract each other when the current is in the same direction and repel each other when the currents are in the opposite direction
- Force per unit length on conductor
If the conductor is stationary and the field is changing (varying), then emf induced in it. Such an emf is known as:
Answer (Detailed Solution Below)
Electromagnetic Theory Question 13 Detailed Solution
Download Solution PDFDynamically induced EMF: When the conductor is rotating and the field is stationary, then the emf induced in the conductor is called dynamically induced EMF.
Ex: DC Generator, AC generator
Static induced EMF: When the conductor is stationary and the field is changing (varying) then the emf induced in the conductor is called static induced EMF.
Ex: TransformerFaraday’s laws of electromagnetic induction are related to:
Answer (Detailed Solution Below)
Electromagnetic Theory Question 14 Detailed Solution
Download Solution PDFFaraday’s first law of electromagnetic induction states that whenever a conductor is placed in a varying magnetic field, emf is induced which is called induced emf. If the conductor circuit is closed, the current will also circulate through the circuit and this current is called induced current.
Faraday's second law of electromagnetic induction states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil. The flux linkage of the coil is the product of number of turns in the coil and flux associated with the coil.
These laws are related to the emf of a generator.The potential inside a charged hollow sphere is __________.
Answer (Detailed Solution Below)
Electromagnetic Theory Question 15 Detailed Solution
Download Solution PDF- The electric field inside a conducting sphere is zero, so the potential remains constant at the value it reaches the surface.
- When a conductor is at equilibrium, the electric field inside it is constrained to be zero.
- Since the electric field is equal to the rate of change of potential, this implies that the voltage inside a conductor at equilibrium is constrained to be constant at the value it reaches the surface of the conductor.
- A good example is the charged conducting sphere, but the principle applies to all conductors at equilibrium.