Test: Electromagnetic Fields Theory- 2 - Electrical Engineering (EE) MCQ

Two infinite parallel metal plates are charged with an equal surface charge density of the same polarity. The equal surface charge densities are having the same charge either positive or negative. The same charge repels each other, hence the resultant electric field in the gap between the plates is zero.

The capacitance of an isolated sphere is,

The electric dipole moment is a measure of the separation of positive and negative electrical charges. It consists of two equal and opposite charges that are infinitely close together. Its magnitude is equal to the product of the charge and the distance between the charges and having direction from the negative to the positive charge along the line between the charges.

p = qd

The SI unit for electric dipole moment is coulomb-meter

Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet (ferromagnetic) are used to make a permanent magnet.

Cobalt steel contains about 35% of cobalt. It has a very good magnetic property that is why it is used for making permanent magnets.

Copper, Silver, Diamond are examples of diamagnetic materials.

Diamagnetic materials are slightly repelled by a magnetic field and the material does not retain the magnetic properties when the external field is removed.

Given that,

Electric field (E) = 30000 V/mm

Breakdown voltage (V) = 33 kV

The inductance of a coil is L = λ/I

Where, λ is flux linkage in weber-turns

I is current in amperes

According to Right-hand thumb rule, imagine that you are holding a current carrying wire in your right hand so that the thumb points in the direction of the current, then the direction in which the fingers wrap the wire will represent the direction of magnetic lines of force.

Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. It is the degree of magnetization that a material obtains in response to an applied magnetic field.

It is a constant of proportionality that exists between magnetic flux density and magnetic field intensity.

B = μH

The units of magnetic permeability are henry per meter

Given that,

Inductance of a coil (L) = 0.8 mH

Current (I) = 2 A

Change in current = 2 – (–2) = 4

Given that, L₁ = 2 mH, L₂ = 4 mH, M = 0.15 mH

The equivalent of two coils in series connection for differential coupling is

L_eq = L₁ + L₂ - 2M = 2 + 4 – 2 (0.15) = 5.7 mH

This power of magnetism after the applied magnetism is removed is called retentivity of a substance.

Materials which are required to retain their magnetism will have high retentivity and as such are used to make permanent magnets.

Self-inductance of a coil is defined as the ratio of self-induced emf to the rate of change of current in the coil.

Higher the self-inductance of a coil, longer the delay in establishing a steady current through it.

The air gap in magnetic circuit means the magnetic resistance, i.e. reluctance to the magnetic flux density. Hence the air gap indicates the increase in reluctance.

Magnetic pole strength is a measure of the force exerted by one face of a magnet on a face of another magnet when both magnets are represented by equal and opposite poles.

Weber is the MKS rationalized unit of magnetic pole strength quantity.

Given that,

Current (I) = Changed form 2 A to 4 A

Change in current = 2 A

Time (t) = 0.05

Emf (e) = 8 V

From the given circuit, 

Soft magnetic materials are those materials that are easily magnetized and demagnetized.

Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. It is the degree of magnetization that a material obtains in response to an applied magnetic field. Hence it should be high for soft magnetic materials.

Coercive field or coercive force is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Hence it should be low for soft magnetic materials.