Electromagnetic Theory - Unit 3 - Question Bank

1.Define magnetic field strength.

The magnetic field strength (H) is a vector having the same direction as magnetic flux density. H=B/µ

2.Write down the expression for magnetic field at the centre of the circular coil.

H = I/2a.

3.Write he expression for field intensity due to a toroid carrying a filamentary current I

H=NI / 2ïR

4.Give the relation between magnetic flux density and magnetic field intensity.

B =µ H

5.Define inductance.

The inductance of a conductor is defined as the ratio of the linking magnetic flux to the current producing the flux. L = Nφ / I

6.Give the formula to find the force between two parallel current carrying conductors.

F=µI 1I2/ 2ðR

7.Give the expression for torque experienced by a current carrying loop situated in a magnetic field.

T = IABsinθ

8.What is torque on a solenoid?

T = NIABsin θ

9.Write the expression for energy density in electrostatic field.

W=1 / 2 εE2

10.What is the expression for energy stored in a magnetic field?

W = ½ LI2

11.What is energy density in magnetic field?

W = ½ µH2

12.Distinguish between solenoid and toroid.

Solenoid is a cylindrically shaped coil consisting of a large number of closely spaced turns of insulated wire wound usually on a non magnetic frame. If a long slender solenoid is bent into the form of a ring and there by closed on itself it becomes a toroid.

13.What is lorentz force?

Lorentz force is the force experienced by the test charge .It is maximum if the direction of movement of charge is perpendicular to the orientation of field lines.

14.State Biot –Savarts law.

It states that the magnetic flux density at any point due to current element is proportional to the current element and sine of the angle between the elemental length and inversely proportional to the square of the distance between them

dB=µ Idl sinθ / 4πr2

15.State amperes circuital law.

Magnetic field intensity around a closed path is equal to the current enclosed by the path.


16.Give the force on a current element.

dF = BIdlsinθ

17.Define magnetic vector potential.

It is defined as that quantity whose curl gives the magnetic flux density.

B=▼ x A=µ / 4πJ/r dv web/m2

18..Define magnetic moment.

Magnetic moment is defined as the maximum torque per magnetic induction of flux density. m=IA

19.Give the relation between electric field intensity and electric flux density.

D=Eε C/m2

 20. Define current density.

Current density is defined as the current per unit area. J= I/A Amp/m2


1. Calculate field using Ampere’s Circuital law for infinitely long solenoid

2. Determine the Magnetic flux density B caused by a finite length current filament of length ‘L’ on the z-axis at a distance ‘d’ from the origin.

3. Explain how to calculate field using Ampere’s Circuital Law for symmetrical current distribution for infinitely long filament carrying current I

4. Explain how to calculate field using Ampere’s Circuital Law for symmetrical current  distribution for coaxial cable.
      a) state and explain ampere’s Law
     b) A current filament of 5.0 A in the ay direction is parallel to the y axis at x = 2m, z = - 2m. Find H at the origin.

5. Define and explain Vector Magnetic Potential.

6. A circular loop of radius ‘b’ in the XY plane and carries a current ‘I’, as depicted in figure. Obtain an expression for the magnetic flux density at a point on the positive z  axis.

7. Apply Ampere’s Circuital Law to the perimeter of a differential surface element and obtain the point form of ampere’s circuital Law.