MCQs on Electromagnetic Fields

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01․ A solid sphere made of insulating material has a radius R and has a total charge Q distributed uniformly in its volume. What is the magnitude of electric field intensity, E, at a distance r (o less than r less than R) inside the sphere
3 Qr/(4 π εo R3).
Q/(4 π εo r3).
Qr/(4 π εo R3).
QR/(4π εo r3).

Let we assume a Gaussian surface inside the sphere (x < R) From Gauss’s law ψ = Q enclosed \ Again Qenclosed = surface integral of (D.ds) \

02․ For a line characteristic impedance zo terminated is load zo/3, the reflection coefficient is
– 1/3.
– ½.


03․ In frec space E (z,t) = 103 sin(ωt - βz) uy v/m. What is the value of H (z,t)
(103/377) sin(ωt - β z)(-ux) A/m.
(103/377) cos(ωt - β z)(-ux) A/m.
(103/377) sin(ωt - β z)(-uy) A/m.
None of above.

Direction of wave propagation (+z). So E × H must be (+z) direction. Therefore E × H must be – ux Now Ey/Hx = ηo = 377 (As free space) Hx = 103/377 (A/m).

04․ Magnetic flux density emerging out of a closed surface is
depends on magnetic movements inside the closed surface.
depends on magnetic movements outside the closed surface

Magnetic flux through a surface is zero because all the field lines that enter the surface exit it.

05․ Which of the following is zero in relation to electromagnetic fields?
Grad div A.
Div grad V.
Div curl A.
Curl curl A.

We know

06․ Magnetic current is composed of which of the following?
Both conduction and displacement current.
Only displacement current.
Only conduction current.
None of the above.

Displacement current flows inside the capacitor due to accumulation of charges on the capacitor walls and conduction current flows due to the flow of electrons due to some potential difference.

07․ What is the value of magnetic vector potential due to an infinitesimally small current element, evaluated at infinite distance from it?
Depends on strength of current element.

Magnetic vector potential due to an infinitesimally small current element is inversely proportional to the distance of the point under consideration.

08․ A long straight wire carries a current I = 10A. At what distance is the magnetic field H = 1A/m?
1.19 m.
1.29 m.
1.59 m.
1.39 m.

09․ How much current must flow in a loop of radius 1m to produce a magnetic field of 1 mA/m?
2 mA.
2.5 mA.
1.5 mA.

10․ The magnetic intensity in A/m at the centre of circular coil of diameter 1m and carrying a current of 2A is