Electromagnetic Theory MCQ || Electromagnetic Theory Questions and Answers

Answer.4. 2

Explanation

The magnetic field intensity (H) of a circular coil is given by

H = I/2R

Where I is the current flow through the coil

R is the radius of the circular coil

Given

Current (I) = 2 A

Diameter = 1 m

Radius (R) = 0.5 m

Magnetic field intensity = H = 2/2 × 0.5

H = 2 A/m

Answer.4. Henry^-1

Explanation

The SI unit for magnetic reluctance is Henry^-1

Magnetic Units:

Answer.2. Ferromagnetic material

Explanation

Ferromagnetic substance or material is used for the generation of ultrasonic waves by using the magnetostriction effect.

Magnetostriction Effect:

• When a magnetic field is applied parallel to the length of a ferromagnetic rod made of a material such as iron or nickel, a small elongation or contraction occurs in its length. This is known as magnetostriction.
• The change in length depends on the intensity of the applied magnetic field and the nature of the ferromagnetic material.
• The change in length is independent of the direction of the field.

Answer.2. Change in flux

Explanation

In Lenz’s law, the induced emf ‘e’ opposes the change (increase or decrease) in flux.

Lenz’s law: When a voltage is generated by a change in magnetic flux according to Faraday’s law, the polarity of the induced voltage is such that it produces a current whose magnetic field opposes the change which produces it.

The induced emf is given by the rate of change of magnetic flux linked with the circuit i.e.

e = −dφ/dt

Where dΦ = change in magnetic flux and e = induced e.m.f.

Answer.1. 1/r

Explanation

Electric field due to an infinitely long straight conductor is

$E = \frac{\lambda }{{2\pi {_o}r}}{\rm{\;}}$

Where

λ = linear charge density

r = radius of the cylinder

ε_o = permittivity of free space.

From the above equation, it is clear that the electric field of an infinitely long straight wire is proportional to 1/r. Hence option 1 is correct.

Answer.3. Zero

Explanation

The electric field and charge density in a perfect conductor are both zero, and thus the conductor is an equipotential and is electroneutral. If E is zero, the charge density in the ideal conductor is zero.

Answer.4. All of the above

Explanation

The 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 exerted on one wire due to currents through two wires is inversely proportional to the distance between them. Thus the force becomes half if the distance between the wires is doubled.
• The attractive force between two parallel current-carrying wires is  proportional to the product of the two currents.

Force per unit length on conductor

$\frac{F}{l}=~\frac{{{\mu }_{0}}}{2\pi }\frac{{{i}_{1}}{{i}_{2}}}{d}$

It satisfies newton’s third law.

Answer.1. Magnetic Field

Explanation

Magnetic Field is analogous to the electric field in magnetic circuits

Magnetic circuits are analogous to electric circuits. Some of the quantities are given below.

Answer.4. Polarization

Explanation

Polarization of light occurs when light is reflected, refracted, and scattered.  The direction of vibration of particles is a property associated with waves. Since light shows the vibration of the electric and magnetic field through polarization, the wave nature of light is concluded from polarization.

Answer.3. 2T

Explanation

Given

N = 100
I = 5 A
L = 2πr = 2π × 5 × 10^-2 m

Magnetic Field Strength H = NI/L

H = (100 × 5)/2π × 5 × 10^-2

H = 5000/π

The net Magnetic Field Density (B_net) is given by

B_net = μ₀μ_rH

Where

μ₀ is absolute permeability. = 4π  × 10^-7m

μ_r is relative permeability = 1000 (given)

B_net = (4π  × 10^-7m × 1000 × 5000)/π

B_net = 2T