Electromagnetic theory miscellaneous


Electromagnetic theory miscellaneous

Electromagnetic Theory

  1. The velocity of electromagnetic waves in free space—









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    The velocity of electromagnetic waves in free space is independent of frequency.

    Correct Option: C

    The velocity of electromagnetic waves in free space is independent of frequency.


  1. The value of ∮ di along a circle of radius 2 units is— ƒ









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    ∮ dl is always zero whatever may be the closed path it is so because dl is an element of displacement displacement (not of simply length) and around a closed path is starting at one point and reaching back over there, net displacement is zero and hence ∮ dI = 0.

    Correct Option: A

    ∮ dl is always zero whatever may be the closed path it is so because dl is an element of displacement displacement (not of simply length) and around a closed path is starting at one point and reaching back over there, net displacement is zero and hence ∮ dI = 0.



  1. If the vectors A and B are conservative then—









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    A and B both are conservative field vectors.
    Therefre, ∇ × A = 0 and ∇ × B is also zero.
    Now ∇. ( A × B) = – ∇. ∇ A + ∇. ∇ × B = 0
    Hence, ( A × B) is solenoidal.

    Correct Option: A

    A and B both are conservative field vectors.
    Therefre, ∇ × A = 0 and ∇ × B is also zero.
    Now ∇. ( A × B) = – ∇. ∇ A + ∇. ∇ × B = 0
    Hence, ( A × B) is solenoidal.


  1. If
    n
    is the polarization vector and
    k
    is the direction of propagation of a plane electromagnetic wave, then—









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    The polarization vector and direction of travel are perpendicular to each other. n. k = 0

    Correct Option: C

    The polarization vector and direction of travel are perpendicular to each other. n. k = 0



  1. A straight wire of circular cross-section carries a direct current I, as shown in figure below. If R is the resistance per unit length of the wire, then the Poynting vector at the surface of the wire will be—









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    R is the resistance per unit length and I is the current flowing. Therefore, power loss occurring in the conductor per unit length is I2R. This power is furnished on E and H fields at the surface of the wire. According to Poynting theorem E × H is the power flow per unit area. Since the power is fed from outside through the cylindrical surface of the conductor, E × H at every point on the surface is radial and directed into the surface. Therefore, Poynting vector is

    I2R(−n)
    =
    I2R
    (−n)
    surface area2∏r × 1

    where n is the unit radial vector directed outward.

    Correct Option: B

    R is the resistance per unit length and I is the current flowing. Therefore, power loss occurring in the conductor per unit length is I2R. This power is furnished on E and H fields at the surface of the wire. According to Poynting theorem E × H is the power flow per unit area. Since the power is fed from outside through the cylindrical surface of the conductor, E × H at every point on the surface is radial and directed into the surface. Therefore, Poynting vector is

    I2R(−n)
    =
    I2R
    (−n)
    surface area2∏r × 1

    where n is the unit radial vector directed outward.