Ques.1. Find H = ___________ A/m at the center of a circular coil of diameter 1 m and carrying a current of 2 A.

0.6366

0.1636

6.366

2

Answer.4. 2

Explanation:-

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

$H = \frac{I}{{2 R}}$

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 $H = \frac{2}{{2 \times 0.5}} = 2\;A/m$

Common Mistake:

The magnetic field intensity (H) of a circular coil is given by $H = \frac{I}{{2 R}}$

The magnetic field intensity (H) of a straight conductor is given by $H = \frac{I}{{2\pi R}}$

Ques.2. Hysteresis loss is ________ proportional to the area under the hysteresis curve. Also, it is ________ proportional to the number of cycles of magnetization per second:

Directly, inversely

Inversely, directly

Directly, directly

Inversely, inversely

Answer.3. Directly, directly

Explanation:-

The hysteresis loss is directly proportional to the area under the hysteresis curve i.e. area of the hysteresis loop. It is directly proportional to frequency i.e. number of cycles of magnetization per second.

Hysteresis loss occurring in a material is,

W_{h} = η × B_{m}^{1.6} × f × V

Where η is hysteresis constant

f is frequency or number of cycles per second

B_{m} is the magnetic flux density

V is the volume of the core

Hence it is directly proportional to the number of cycles of magnetization per second

Ques.3. Which of the following materials is used for the generation of ultrasonic waves by using magnetostriction effect?

Paramagnetic material

Ferromagnetic material

Diamagnetic materials

Both paramagnetic and diamagnetic material

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.

Ques.4. If a circular conductor carries a current of ‘I’ ampere having radius ‘r’ meter, then the magnetizing force at the center of the coil is given by ;

I/4r AT/m

I/r AT/m

I/2r AT/m

I/2r AT/wb

Answer.3. I/2r AT/m

Explanation:-

Magnetic Field Strength (H) gives the quantitative measure of the strongness or weakness of the magnetic field.

H = B/μ_{o}

Where

B = Magnetic Flux Density

μ_{o }= Vacuum Permeability

The magnetic Field strength at the center of circular loop carrying current I is given by

B = μ_{o}I/2r

B/μ_{o} = I/2r

H = I/2r At/m

Where r = Radius

Ques.5. What is the relationship between magnetic field strength and current density?

Gauss’ law of Magnetostatics (non-existence of magnetic monopole)

Ques.6. Two identical coils A and B of 1000 turns each lie in the parallel plane such that 80% of the flux produced by one coil links with the other. If a current of 5 A flowing in A produces a flux of 0.05 mWb, then the flux linking with coil B is:

0.4 mWb

0.04 mWb

4 mWb

0.004 mWb

Answer.2. 0.04 mWb

Explanation:-

Consider two coils having self-inductance L1 and L2 placed very close to each other. Let the number of turns of the two coils be N_{1} and N_{2} respectively. Let coil A carries current I1 and coil B carries current I_{2}.

Due to current I1, the flux produced is ϕ1 which links with both the coils. Then the mutual inductance between two coils can be written as

$M = \frac{{{N_1}{\phi _{12}}}}{{{I_1}}}$

Here, ϕ_{12} is the part of the flux ϕ1 linking with the coil 2

Calculation:

Flux produced in coil X (ϕ1) = 0.05 mWb

As we are just required to find the flux linked with the second coil, and we are given that 80% of the flux produced by one coil links with the other.

∴ Flux linked with Y (ϕ12) = 80% of flux produced in coil 1

= 0.05 × 0.8 mWb

0.04 mWb

Ques.7. The current flowing through a coil of 2 H inductance is decreasing at a rate of 4 A/s. What will be the induced EMF in the coil?