MCQs on Electromagnetic Fields

01․ Find H for centre of solenoid having finite length d = 1 unit where N = no of turns = 500, I = 2 A.

From Biot Savarts law, magnetic field intensity for a solenoid is given as H = NI/u_x.

02․ A magnetic vector potential is given by the expression A = (- cos x) (cos y) u_z. The flux density at the origin is

B = curl of A Since flux density at origin (x = 0, y = 0) so B = 0.

03․ A circular loop has its radius increasing at a rate of 2 m/s. The loop placed perpendicular to a constant magnetic field of 0.5 wb/m². When the radius of the loop is 4 m. the emf induced in the will be

Area of the loop A = π r² Magnetic of unit emf induced dQ/dt.

04․ A magnetic field B = 5 × 10^-2 u_z T exerts a force on 0.02 m conductor along the x-axis. The conductor carried a current of 5 mA in the – u_x direction. What force must be applied to the conductor to hold it in position

F = IL × B Applied forced F_a = - (IL × B) Since F_a force hold conductor position. So the force will be opposed.

05․ The hysteresis loop of a magnetic material has an area of 5 cm² with the scale given as 1 cm = 2 AT and 1 cm = 50 mwb At 50 Hz; the total hysteresis loss is

Power loss in watt given as, P_h = W _h v.f Where W_h = energy density loss V = Volume of material In this case, W_h.V = area of hysteresis loop = 5 cm².

06․ A wire 1 m long carries a current of 5A and is at an angle of 30^o with B = 1.5 wb/m². Magnitude of force is

F = BIL sinθ.

07․ A negative point charge q = - 40 nC is moving with velocity of 6 × 10⁶ m/s in a direction specited by unit vector u_y + 0.6 u_z. Find the magnitude of force vector on the moving particle by the field B = 2 u_x + 3 u_y + 5 u_z mT and E = 2 u_x - 3 u_y + 5 u_z KV/m

Apply F = Q(E + V × B).

08․ The Kirchhoff’s current law is implict in expression

Current at a node is zero, current entering = current leaving. So, surface integral of (j.ds) = 0.

09․ The magnetic field at any point on the axis of current carrying circular coil will be

With coil x – y plane, the field will be in u_z direction.

10․ A coil of 300 turns is wound on a non magnetic core having a mean circumference of 300 mm and a cross sectional area of 300 mm². The inductance of the coil corresponding to a magnetizing current of 6 A will be

Inductance of coil,