Electromagnetic Field Theory - GATE practice papers - Electronics & Communication

1)   Which among the following statements is/are precise in accordance to distortionless line?

A. A lossless line is also a distortionless line
B. A distortionless line is not necessarily a lossless line
(Marks : 02)

- Published on 19 Oct 15

a. A is true & B is false
b. A is false & Bis true
c. Both A & B are true
d. Both A & B are false
Answer  Explanation 

ANSWER: Both A & B are true

Explanation:
The conductors in the lossless line are perfect and the dielectric medium that separates them is absolutely lossless.
Besides this, a transmission line where the value of an attenuation constant is independent of frequency & phase constant is linearly dependent on frequency.
Hence, it is obvious that a lossless line can also be a distortionless line but a distortionless line cannot be essentially a lossless line.


2)   Which among the below given statements are correct in accordance to the properties of a conductor?

A. The static electric field intensity at the surface of conductor is directed parallel to the surface.
B. The static electric field intensity at the surface of conductor is directed perpendicular to the surface.
(Marks : 02)

- Published on 19 Oct 15

a. Only A is correct
b. Only B is correct
c. Both A & B are correct
d. Both A & B are incorrect
Answer  Explanation 

ANSWER: Only B is correct

Explanation:
Conductor develops an equal potential throughout the surface and the static electric field intensity within the inner portion of a conductor is zero. Thus, the properties of a conductor implies that the static electric field intensity over the surface of a conductor is directed equally and normal (perpendicular) to the surface.


3)   How can the total charge enclosed by the closed or covered surface be expressed using Gauss's law ? (Marks : 02)
- Published on 19 Oct 15

a. By the line integral of the charge density
b. By the surface integral of the charge density
c. By the Volume integral of the charge density
d. None of the above
Answer  Explanation 

ANSWER: By the Volume integral of the charge density

Explanation:
Guass's law states that the total flux over the outer closed surface is always equivalent to the total charge within the surface.
Similarly, Guass's law can also be defined in terms of volume integral which states that the total charge present over the closed surface is equal to the volume integral function of the charge density.


4)   Which among the below mentioned operators is supposed to be zero so as to justify the scalar field to be harmonic? (Marks : 01)
- Published on 19 Oct 15

a. Gradient
b. Curl
c. Laplacian
d. Divergence
Answer  Explanation 

ANSWER: Laplacian

Explanation:
A function is said to be harmonic only when its laplacian operator value ▼2f is zero. Similarly, a scalar field is also said to be harmonic only when its laplacian operator becomes zero despite the other operators.


5)   Which conditions are mandatory to get satisfied for the formation of a sphere ? (Marks : 01)
- Published on 19 Oct 15

a. 0 ≤ θ ≤ π , 0 ≤ Ф ≤ 2 π & r = constant
b. Ф = change , r = change & θ = constant
c. r → ∞ , 0 ≤ θ ≤ 2π & Ф = constant
d. Ф → ∞ , 0 ≤ θ ≤ 2π & r= constant
Answer  Explanation 

ANSWER: 0 ≤ θ ≤ π , 0 ≤ Ф ≤ 2 π & r = constant

Explanation:
A sphere is formed only when the value of an angle vector originated due to Z-axis and radius vector lies between zero and π; and the value of angle vector between X-axis & radius vector projection over XY plane is greater than zero but less than or equal to 2π ,by keeping radius vector as a constant


6)   How is the distance defined between two radical planes of the spheres at angles Ø and (Ø + dØ ) ? (Marks : 01)
- Published on 19 Oct 15

a. r sin θ dФ
b. sin θ dФ
c. r dФ
d. r + sin θ dФ
Answer  Explanation 

ANSWER: r sin θ dФ

Explanation:
The locus of points which comprises similar powers corresponding to the two spheres is known as radical plane.
Therefore, the distance between two radical planes of the spheres is equal to the product of radius vector measured from Z-axis, sine angle between Z-axis & radius vector and the angle between X-axis and radius vector projection in XY plane.


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